1-Put the mouth guard into boiling hot water for about 2-3 minutes
2- Remove the mouth guard out the boiling water and then dip it in cold water for 2 seconds.
3-Put the mouth guard into your mouth and suck as much air as you can , and bite down. It should form the shape of your teeth within.
Finally put the mouth guard into cold water for 5 minutes and here you go , new mouth guard shaped to your teeth.