Ask HN: How to fix issue and find the origin of bug in codebase?

I wondered how you people approach a bug problem in the issue section. I have never done these things. Since last week, I've been trying to understand the bug's real issue/origin. I couldn't solve it. Initially, I used git bisect and looked into commits & code. I still couldn't figure it out.

If I could understand how you approach these bugs and how they are fixed, what method do you use, and how do you look at the code to fix them? Then, honestly, it would be invaluable to me.

Also, if you could please share any resources or articles, I would be very interested in looking at them; I could take some lessons from them.

Thanks.