If its just the dropouts that are bent its a easy fix.
Park makes a alignment tool
https://www.parktool.com/blog/repair...pout-alignment
But you can make your own using a axel cut in half and some wheel nuts.
The the chain and seat stays are out that's a bit different. There's a good article on Sheldon brown's site.
I don't know if your city has a bike co-op. But sometimes they have frame alignment tools.