How-to guide
How Do I Train ChatGPT on My Business?
Upload your docs, build a Custom GPT, and get answers in your brand voice. No technical knowledge required.
Book a discovery callA quick note on "training"
"Training ChatGPT on your business" doesn't mean retraining the underlying AI model - that would require significant data and engineering resource. What it means in practice is giving ChatGPT persistent access to your business context: your documents, your tone, your products, your processes. You're configuring the tool, not modifying the model.
There are three ways to do this, ranging from the simplest (Custom Instructions, a two-minute setup, no file uploads) to the most powerful (Custom GPTs, which give ChatGPT a persistent knowledge base built from your actual documents). This guide covers all three in order of complexity.
You don't need to be technical. You need a ChatGPT Plus or Team subscription for the more powerful methods, and your business documents in a readable format.
What you need
Documents that work well - and ones that don't
You don't need a large library to get started. Two or three well-written documents - a brand voice guide, a service description, and an FAQ - will produce noticeably better outputs than a generic ChatGPT session.
Works well
Brand voice or tone of voice guide
Teaches the GPT how you write and what language to use
Product and service descriptions
Gives the GPT accurate, up-to-date detail to reference
FAQ document
Pre-loads common questions so answers are consistent
Past proposals or case studies
Shows the GPT your positioning and how you frame value
Standard email templates
Helps the GPT match your communication style precisely
Process or SOP documents
Lets the GPT walk through your standard procedures accurately
Pricing structure (non-confidential tiers)
Enables accurate answers to pricing questions
Avoid or handle carefully
Scanned PDFs (image-only)
ChatGPT reads text - it can't extract text from scanned images
Files over 512MB
The file size limit per upload - split large documents
Client names and contact data
Don't expose personal data to a shared or link-accessible GPT
Financial statements with sensitive figures
Internal financials shouldn't be in a shared tool
Anything covered by an NDA
Uploading NDA-covered material to OpenAI's servers may breach it
Highly formatted spreadsheets
Complex table structures often parse poorly and cause errors
Step-by-step setup
Three methods, from simplest to most powerful
Start with Method 1 if you want the full capability. Start with Method 3 if you want something working in under five minutes today.
Best for: Ongoing use by you or your team - the best option for most businesses
Needs: ChatGPT Plus (£16/mo) or Team (£25/user/mo)
Open the Custom GPT builder
Go to chat.openai.com. Click your profile name in the top right corner, then select My GPTs from the dropdown. Click Create a GPT.
Describe your GPT in plain English
The Create tab opens a chat with the GPT builder. Tell it what you want: your business name, what the GPT should help with, and the tone it should use. Example: "Build a GPT for Reformat Labs, an AI consultancy. It should help write client emails, proposals, and social posts in our voice - professional but plain-spoken, no jargon."
Switch to Configure and write your instructions
Click the Configure tab. The Instructions field is the most important part - this is where you write a detailed brief. Include: what your business does, your tone and style, what the GPT should and shouldn't do, and any specific rules (e.g. "always suggest booking a call rather than giving a definitive price").
Upload your knowledge documents
Under the Knowledge heading, click Upload files. Drag in your documents - brand guide, product descriptions, FAQ, past proposals. You can upload up to 20 files. PDF and Word (.docx) files work best. Plain text (.txt) also works well.
Test it with real questions
The Preview panel on the right shows your GPT as it will appear. Ask it questions you'd expect clients or your team to ask. Check: are the answers accurate? Does the tone match your brand? Does it make up anything that isn't in your documents?
Save and choose your sharing setting
Click Save in the top right. You'll be asked who can use this GPT: Only me (private), Anyone with a link (shareable), or Everyone (public in the GPT Store). For team use, choose Anyone with a link and share the URL. For sensitive content, keep it private.
PRO TIP
Write your Instructions as if briefing a new employee who is excellent at following instructions but knows nothing about your business. The more specific you are, the better the output.
Best for: Ongoing work in a specific area - e.g. a project folder for client proposals
Needs: ChatGPT Plus or Team
Create a new Project
In the ChatGPT sidebar, look for Projects and click the + icon or New project. Give it a name that reflects the work area, e.g. "Client Proposals" or "Marketing Content".
Add files to the project
Inside the project, click the paperclip or files icon to add documents. These files are available in every conversation within the project - you don't need to re-upload each time.
Set custom instructions for the project
Projects support project-level instructions separate from your global custom instructions. Add a brief for how conversations in this project should behave.
Start conversations within the project
Any new chat started inside the project automatically has access to the files and instructions you've set. The project sidebar shows all previous conversations in that context.
PRO TIP
Projects are useful when you want document access without the overhead of building a full Custom GPT. Good for a focused use case - not ideal if you want to share access with others.
Best for: Persistent context in every chat without file uploads - best for tone and business facts
Needs: ChatGPT free tier or above
Open Custom Instructions
Click your profile name at the bottom left of the ChatGPT interface. Select Customize ChatGPT (or Custom Instructions). This opens two text fields.
Fill in the first field - About you
Paste a brief description of your business: what you do, who you serve, your tone of voice, and any standing preferences. This context is automatically included in every conversation.
Fill in the second field - How to respond
Describe how you want ChatGPT to behave: format preferences, level of detail, whether to ask clarifying questions, what to avoid. Example: "Use plain English. No bullet points unless I ask. Always suggest a next action at the end."
Save and test
Click Save. Start a new conversation and check that the context is being applied - ask it to write something in your brand voice and see if it matches without further prompting.
PRO TIP
Custom Instructions can't hold documents, only text. Paste the most important parts of your brand guide directly into the field rather than referencing a document. 1,500 characters per field.
Keeping it updated
Your GPT doesn't update itself
A Custom GPT's knowledge base is a snapshot of your documents at the time of upload. It doesn't automatically know about changes to your pricing, services, or brand unless you update it. These are the key moments to review and update your setup.
When your services or pricing change
Re-upload your product/service description and pricing document. Delete the old version from the knowledge base first to avoid the GPT drawing on contradictory information.
When your brand voice evolves
Update your Instructions field directly - it's editable at any time. You can also update and re-upload the brand guide document.
Quarterly review
Set a recurring reminder to review what's in the knowledge base. Remove outdated documents, update anything that's changed, and run a test conversation to check output quality.
When you notice wrong answers
If the GPT starts giving inaccurate answers, it usually means the source document has changed or was ambiguous. Update the relevant document and re-upload. Add an explicit instruction to override any specific misunderstanding.
When you add new products or services
Add a new document covering the new offering. Don't try to cram everything into one mega-document - separate files by topic make it easier to update individual sections later.
Good practice
Keep a single "Master context document" - a text file with your key business facts, services, pricing tiers, and tone guidelines. When anything changes, update this file and re-upload it to your GPT. It's faster than tracking which individual document needs updating.
Privacy notes
What you should and shouldn't upload
Your uploaded documents are stored on OpenAI's servers. The data handling depends on your subscription tier - and it matters for what you choose to include.
Training: Conversations and data may be used to improve OpenAI models
DPA: No
Don't upload confidential business documents on the free tier
Training: You can opt out of model training in Settings. Not opted out by default
DPA: No formal DPA
Turn off model training before uploading business documents. Go to Settings - Data controls - Improve the model for everyone: off
Training: Conversations and files are not used for training by default
DPA: Terms include organisational data handling commitments
Appropriate for most business document use cases. Still avoid uploading personal client data
Training: No model training on your data. Full data isolation
DPA: Formal DPA available
Suitable for sensitive business information. Consult your legal team for highly regulated sectors
Never upload to any ChatGPT plan
Client personal data (names, contact details, addresses) - Financial statements containing sensitive figures or forecasts - Legal documents covered by NDA or privilege - Patient, student, or employee records - Anything where a data breach would have serious consequences
Want this set up properly?
We build Custom GPTs and AI workflows tailored to your business
Beyond the out-of-the-box Custom GPT setup, we can build more sophisticated workflows - connecting your documents to AI tools with better retrieval, automation, and integration with your existing systems. Book a call to discuss what's right for your business.
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