K3500 dually fender removal?

[Idahoan6-0]

I have a '92 K3500 I'm working to part out, and I have someone who wants one of the dually fenders. I got the damaged one they didn't want off, as I wanted to make sure I was removing it properly, and it appears to have some sort of self tapping bolts that goes into the fender (?). How are these supposed to be removed? I'm guessing that self tapping screw/bolt is supposed to stay in the fender, but how would i stop those from turning when the nut has a light coating of rust holding it in place? Any help is appreciated.