Bent rims can be fixed as long as they are steel rims. Cast rims are made from hardened materials, and once they are bent, the material integrity is severely compromised. Steel spoked wheels that are out of round can usually be fixed by truing the wheel. This can take the wobble out of the wheel. The wheel is placed on a truing stand to determine where the issue is on the rim, then the spoke tension is adjusted accordingly to straighten the wheel. If you have a spoked steel rim that has a dent in it due to a severe impact, and the side of the rim is bent inward, it is better to just replace the rim at that point. You can spend a ton of time trying to repair that dent, but the rim is never going to run true.