High Quality Custom mouth guard

Put it in a cup of warm water(70~80C) till soft for 10~20 seconds.
If it is soft, insert it into your upper teeth in the mouth.
To memorize your mold of teeth, bite it for 10~15 seconds.
If it is fitted to your teeth, clean it with water & use it.
If it is not good for your mouth, you can fix it again as follows from No.1