Declare a variable to change MC value

hello,

I want to declare a variable in the main timeline that will change a value in a movieClip.

I have
var x_alpha:int = 1; (in the main timeline)

“squere” (a movieclip) that is inside “Shapes” (another movieClip)

I can’t write inside “Shapes”

squere.alpha = x_alpha;

what do I do?