Put a pot of water onto a stove top and turn the stove on high.
Wait for the stove to bring the pot to a rolling boil.
Drop the prefit mouth guard into the boiling water and leave it in for 10 to 20 seconds.
Pull the mouth guard out of the water with a pair of tongs or spoon. The hot water softens the rubber, allowing it to be reshaped.
Position the mouth guard on your top teeth and firmly bite down. Hold the bite for a few moments, and then remove the mouth guard from your mouth. The mouth guard has now been refit.