Personally I think that looks like Brooklynella with the spots of skin looking like they are coming off. But will need better pic to confirm. Possible that it is beyond the point of return, but for what it is worth, the only readily available cure for Brooklynella is formaline. 1ml per 4 liter of well aerated tank water, fish bathed in it for 30min, do that 3 or 4 times a few days apart with fish being transferred to a new tank/container in between and it should work. But only works in early stages of infection, that looks like the fish might not be strong enough to survive the medicine at this stage.