I recently converted a Raleigh Grand Prix to fixed gear, and used the inner chainring, a 42 tooth ring with three bolt holes. One of my chainring bolts worked its way out while I was riding, and I didn't notice the problem until I threw my chain. Problem is, while the chainring was only attached in two places, the stress placed on it by the chain caused it to warp rotationally (that is, it's very slightly elliptical when viewed from the side of the bike). This is a problem for two reasons: first, I can't maintain proper chain tension this way, and second, more importantly, the holes on the chainring won't line up with the ones on the spider, so I can't install it. I'm pessimistic, but I was wondering if anyone knew of a successful way to bend the chainring back to true before I go hunting for a new one.

If you're very (and I mean Very) good with a hammer you might be able to work it back to round. Otherwise you're SOL, because the odds of finding a replacement ring for that crank aren't too good. You might end up needing a new crank, and maybe a new bottom bracket. Hint, look around at garage sale junkers for the type of crank and chainring you need.

Why don't we see what Sheldon has to say?
https://www.sheldonbrown.com/straighten-chw.html

I've had lots of success with the application of a big rubber mallet.