The event handler shouldn't be static.

public void Form1_ListenToChanges(MyUserControl sender)

And the event subscription should be effected in the Form1 class.

public Form1()
{
    // ...
    this.myUserControl.Value_Change += this.Form1_ListenToChanges;
}

(Form1 has a MyUserControl, right? The code snippet above assumes that it does and that it is this.myUserControl.)

(You can then make the event handler private.)

private void Form1_ListenToChanges(MyUserControl sender)