In versions before 3.7, switching the Game window between window mode and full-screen mode required restarting the application. So if the Game window is in full-screen mode there's no way to move the window, since there is no "window chrome" (there's no window title bar) where you can click your mouse to drag the window around. So I added a whole set of controls to be able to move the Game window. But those controls were clunky, and required that you describe to the application your display configuration. Once you did that, it was easy to move the Game window where you wanted it.
But in 3.7 and later versions the Game window can toggle between window mode and full-screen mode simply by pressing the F11 key. So, if you want to move the Game window to your second display/monitor, you just close the Settings window, press F11 to toggle the Game window into window mode, use your mouse to drag the Game window to the display you want it on, then press F11 again to go back to full-screen mode.
I've received many inquiries about this. So I have been contemplating adding some of that functionality back, as it was admittedly convenient even if no longer necessary.