Feed GPT with own content for creating a support bot

Hi !

I’m new to GPT so please forgive any dumb questions I might ask.
I have a subscription so that I can create my own GPT (support bot) that should use my own content (currently I host my knowledge base in a GitHub repository and write the content in markdown) to be able to answer questions from my users.
My question is: What is the correct way to feed my support bot (I create one now) and are there any good open source tools to transform my markdown files (or other content in future) so that GPT can understand it ?
I saw that there might be an option using Actions API to retrieve content from an external source. Is that the correct way to write an own service that will provide an openAPI REST interface and that service would serve the content ?
Are there other ways to automatically ingest “files” into my GPT and keep it up2date (so without the manual upload using Knowledge) ?