Hello doctor .i'm19. i want to get rid of my genetic double chin by defining just the jawline.is there any exercise i can do by my self for this issue?

Not really: If you are overweight, getting down to a normal weight would minimize the appearance of your double chin, since fat deposits would decrease everywhere. Otherwise, there is no specific exercise that is likely to change your appearance. Some people are bothered enough by specific features like that to eventually consider plastic surgery (liposuction, etc).

No exercise.: Chewing gum or clinching your teeth won't provide spot reductions. Fat distribution for any individual is genetically determined. While exercises can improve local tone they do not provide spot reductions. With exercise you can decrease the total amount of fat on your body but where that fat is laid down and where it is removed from is predetermined by your genetics. Sorry.