1.)Create an integer named x and equate it to 0.
2.) now make a system event "repeating every seconds". In it put time equal to 0.001 seconds(please experiment with the time, I exactly do not remember). Through this event put x=0
3.)now create another event "your touch section". In it, whenever the user touches the screen, add 1 to x
4.) the real game starts. Now make a system event (every tick one). And remember the condition:
If the value of x>2, then make the x equal to 0 and make it do your task like what you want your character to do at double touch hit
Have a nice day