Help figuring out whats wrong with my koi Koi

One of my koi has had a bump over his eye for about 2 years; first noticed opening the pond after the winter. We thought it may have bumped into the heater or an animal had scratched it. This morning, thats how it looked. Later this morning, it seemed to have ruptured returning to how it used to look. Wed like to do something to help it if possible, as well as to help the other fish if this could impact them at some point.

Thanks a lot for your reply.