What you can do is check the repo issues and see if there is something you can do :D
Thanks! From there how do I find the file that the issue is in?
That part's on you. Unit tests will help you sometimes, other times you'll have to trace the flow of execution yourself (or write tests), still other times grep is your best friend. But every situation is different and the only way to learn is by doing.
More on tests as documentation:
Without docs or good tests, it's going to be a matter of search, trial, and error, as Dian is saying.
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