Executing a function in a class from timeline

programming flash
1

I have a class called TestMover and it has a function in it which changes its X position. I would like to execute that function from the main timeline. It worked when I used static function but it threw an error when I tried to change the value of X.

Here is what I tried based on a tutorial I found, it does not work:

TestingClasses.fla

import flash.events.Event;
import classes.TestMover;

addEventListener(Event.ENTER_FRAME,Test);


function Test(event:Event) {
    TestMover.WhatThe();

}

And the class itself:

package classes {
    
    import flash.display.MovieClip;
    
    import flash.events.Event;
    //import classes.TestCustomEvent;    
    

    public class TestMover extends MovieClip {
        
        public static var _INSTANCE:TestMover;
        
        public static var thisX:Number = 0;

        public function TestMover() {
            
            addEventListener(Event.ENTER_FRAME,Test);
            
            
        }
        
        public function Test(event:Event) {
            x=thisX;
            
        }
        
        
        public static function WhatThe() {
            _INSTANCE.x+=10;
            
            
            
        }
        
        public function Test2() {
            trace ("JACK");
            
        }
    }
    
}

What I need to achieve is that when you call the “WhatThe()” function from main timeline, it will move the movieclip this class is attached to on its X axis by a value of 10.

It must also be possible to call an internal function (like Test2()) from the WhatThe() function, right now when I did that it threw an error.

Error this code throws:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at classes::TestMover$/WhatThe()
    at TestingClasses_fla::TestCube_1/Test()