The AI is the one that does the searching by writing queries. The AI decides when calls to its myfiles_browser tool will be useful, which gives the search results.
However, the way file search has been implemented in this myfiles_browser by OpenAI is poor. Knowing when searching is useful is slightly impossible for the AI. Irrelevancy is always returned, at your expense.
The instructions that accompany the tool specification tell the AI that any files there would have been uploaded by the user, the one the AI is talking to, even when they are part of domain knowledge for a specialized AI.
I can directly say that I uploaded the knowledge that is part of a programmer’s Assistant.
You have to overcode this poor orientation, and also tell the AI what it will find when doing a search. This recent post gives a prompt to tune-up the functionality.