I just throw all relevant source code files (entirely) on it, paste the error message and it usually shows me what's going on. Or at least it utters a hunch, which is a good next step to find the error.
I was hoping the GitHub or intelliJ integration of copilot would automate this, especially the latter has excellent static analysis of your code and could automatically provide the AI with relevant context, but they just don't.
Even when asking it to just annotate a function and specifically ask it to document any special cases or oddities it might have, I never got much more than e.g. updateFroobCache() annotated with "updates the froob cache". Wow thanks.
Yes, and eventually, one of us who is doing this will get tired of it enough to automate the process. May even earn them a few bucks.