Function in timeline called fom button question

Hi can anyone give me any advice on how to target a function from a button please?
as im just starting out.

for example i have a graphic i need to rewined (instead of tween backwards)
when the button is clicked it calls this function in timeline

mc_on_stage.onEnterFrame = function() {
if (rewind == true) {
prevFrame();
}
};

Any directiobnn will help thanks

Louis