Access one movieclip from another

Hi

I have a main.fla that contains say 1_mc and a 2_mc.

a1_mc has a button, which when clicked runs a function called say clickedButton.

a2_mc has a marker_mc inside it.

When the clickedButton function runs inside a1_mc, I want the slider_mc to go y=20

I know I can access main.fla timeline by

MovieClip(parent).gotoAndStop("nameOfLabel"); 

I tried

MovieClip(parent).a2_mc.marker_mc.y = 20; 

but it doesn’t work :frowning: