How do I identify where my bugs come from

I'm working on an app, and currently, 2 things dont work: account creation and notifications. I want to find the root of why these errors are occurring, and I want to know if these errors are coming from Firebase, certain settings in Xcode not being checked, or my actual written code not being typed correctly. I've tried to run my issue through ChatGPT many times to pretty much no success, so any help on what to do so I can clear certain areas and make sure the bugs aren't from certain spots, and help me narrow down the issue would be great. Otherwise, if there are other guides or threads I can be linked to, and help me fully break down the issue, that would be great. Thank you for your time reading, and I hope I can get some advice.

How do I identify where my bugs come from
 
 
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