Grammar

I've heard that sometimes using "I were" is correct, not "I was"

Example: "If I were sorry..."
Can this be explained or is this one of the exceptions in English grammar?

I also found this question about "have/has". They asked which one is correct, "has" or "have".
The sentence was: "I'm the only one who have/has the right to do this job."

And the correct answer was: "has" but no one explained why it is...(Could someone please explain, or is it again an exception?)

Also, is there any similar sentences where you can use "have" instead of "has"? (NOTE! there's "I" in it)

Now I'm trippin' (I started to wonder if I wrote correctly: "The correct answer WAS..." or should I have used WERE?)

(As far as Ik, it's USUALLY "have" and "was" when it comes with the "I")

I know I've got many questions up there, sorry 'bout that...
I appreciate your answers

I hope y'all understand my problems, bcause I really wanna know the answers. I'm not a native speaker so I dunno if you'd understand what I wrote (if there is alot of mistakes in my grammar) ?

Thank you in advance and have a good one! ?

Cheers!