What folders and files can I delete in my project that will be rebuilt back

I have a probject that seems really bugged. It thinks there is another IOS advertising version in my project. Plus other isssues im having.

What All can I delete in my project that is safe to do so?
I usually just delete everything inside of lib folder and that usually fixes everyhing.

Wondering what else I can delete. Also files too. So really I need to know what cant I delete.