If the fish is willing to eat, feed him/her.
Just dipping filter media in a mature tank will not automatically transfer sufficient 'good bacteria' to a hospital tank. You need to put the mature media in another filter or aerate a bag of the mature media using an air stone and pump in the hospital tank.
Have you tested the hospital tank water with a test kit to be sure the ammonia and nitrite are at zero?
Just dipping filter media in a mature tank will not automatically transfer sufficient 'good bacteria' to a hospital tank. You need to put the mature media in another filter or aerate a bag of the mature media using an air stone and pump in the hospital tank.
Have you tested the hospital tank water with a test kit to be sure the ammonia and nitrite are at zero?