Movement question

I have 2 mc’s wich are called helper1 and helper 2.
there is an other mc wich is called thumb1.

If user presses thumb1 this MC must go to the Y of helper1._y;
that is done by:

on (press) {
	this.onEnterFrame = function() {
		this._y -= (this._y-_root.helper1._y)*.5;

Now how can I make this MC go to helper2 when it’s pressed again??
If I’m not using the this.onEnterFrame = function thing, I have to keep pressing thumb1 till it reaches helper1’s position… but this prevents me from makeing it go to helper2…

hope this makes any sense!