My best suggestion is to go to a fish store and supply them with the information about your sick goldfish. They might pinpoint the sickness and offer you some medication for your fish.
put the fish under clean water
I don't think you can because when a goldfish is dying you can only clean your bowl or aquarium and the water and hope for luck.
You are killing your goldfish by neglect. Your fishes water must literally stink. It is putrid and needs replacing. The fish has fungus caused by Ammonia in the water, and that is eating away at its...