The main problem here I think is that your function is called Void(). Unless you’re continually calling that from somewhere else in your code it won’t do anything because it won’t be called automatically by the engine. Assuming your 600 pixel value is reasonable for your scene, you probably want to put that code in _process(), like:
func _process(delta):
if global_position.y >= 600:
get_tree().reload_current_scene()
Regarding how to attach code, you want to:
Paste your code into the forum message
Select it
Press the { } button in the forum editor’s toolbar (to format it).