As I understand it;
"gettree().currentscene.addchild(screenclear) "
where it says you want to add a node to your scene. If so, replace it with;
-If this script belongs to the stage root:
add_child(screen_clear)
-But if it belongs to a node one below the root:
get_parent().add_child(screen_clear)
I hope I have helped you. have a nice day.