IMO the best way to feed it is; put the cube / or part of the cube (depending on how many fish you have) into a cup of tank water to defrost it, when it is defrosted pour it into the tank and your fishies will devour it.
I would advise to leave it sitting out to defrost first as lots of liquid comes out of it. As the fish can't consume this liquid, it just pollutes your tank. Leave it until it has thawed, pour off the unwanted liquid, then add to the tank.
Alternatively, you could put it into a net and run the cold tap over it to thaw it, if you don't want to wait. This would drain off the unwanted fluids too.