You could do it like this. The first event moves the objects and the second corrects overshoot. Another option could be to use the MoveTo behavior.
global number toMove=20
global number speed=100
toMove>0
--- sprite: set y to self.y + speed*dt
--- subtract speed*dt from toMove
toMove<0
--- sprite: set yo to self.y +toMove
--- set toMove to 0