Hmm well position is supposed to be a Vector2(xpos, ypos)
Xpos being left-right and Ypos being up-down
So something like Control.position -= Vector2 (0, 900) should do the trick
Also gonna go out on a limb here and assume by Control you mean the node reference to control and not that your code actually has Control.position -= 900
If it does you can get the main scene by using get_tree().get_current_scene()