Set the character sprite's initial Speed to 0.
Set the character sprite's initial Heading to the direction you want it to move.
Inside the button TouchDown event block, set the character sprite's Speed property to a non-zero positive value.
Inside the button TouchUp even block, set the character sprite's Speed to 0.
You will also want to change the character sprite's Interval from 1000 to 100 for smoother movement, most likely.