I wear a ring made out of soft metal daily. I have to try and be conscience of the ring at all times because it can be bent out of shape rather easily. Twice a year I will sit down and take the time to restore the ring to its default shape and all it takes is about a minute.
Items: Brass Hammer, Ring, Ring Mandrel
All I do is take the ring and place it on the ring mandrel. I will pull the ring down as far as it will go and then start tapping the bent portions of the ring to begin shaping it.
Ring out of round.
Every few taps, the ring is pulled down further and further on the mandrel until the ring's form is restored.