Part Replacement for Headlight Bolt/Bushing?/Nut?

Hey folx, I recently bought an 09 prius with only 100k on it and *sucessfully* replaced the water inverter coolant pump on my own. However, while trying to replace the pump I found out that one of the bolts cannot be removed-- it's pretty stuck and then if you can finally get it to move it just spins without loosening, so I think whatever bushing etc it is screwed into has its threads stripped, but I'm not sure what those replacement parts would be or where to get them.

It is stuck enough that the mechanic who had worked on the car before I had bought it had decided to cut the plastic molding around the headlight assembly when replacing it(likely due to a cracked headlight, etc), and then bondo'd it the new headlight assembly that had been cut similarly to the remains of the old one that they couldn't remove.

I really don't want to be in a situation where I end up needing to go to a mechanic for something that would normally be easy to repair on my own just because that one bolt/bushing/nut/whatever is wrecked, but I don't think I can get it out without destroying it at this point. Any advice on extraction and/or how to acquire and replace the parts afterwards are appreciated. I would preferably like to be able to keep the current headlight assembly, as it is function, even though it's bondo'd together.