Basic clarification on Assistants needed

Hi, I’m looking to start working on a bespoke AI for our small company. I’ve got an RAG index working on the chat playground so the chat has all our product info, various other data and it responds well. (via an index and AI search resource)
Ultimately for this application though an Assistant would ultimately be a better choice, as I can develop tools to access various other API’s and pass processes over to a more suitable models if needed.
In the Assistant playground I can see nowhere to set up the index so it points to my Ai search resource data. I can download some files there but file retrieval doesn’t seem to work and there isn’t a button to activate it. I’m not convinced this is the same function anyway.
Is there a way to add RAG to an Assistant?
Is the file download section in the playground ultimately the same thing as I have with the normal chat playground and do I have to activate file retrieval via the API for it to work?