Yes so, when room 2 received the signal of player entered the door, create a signal in that script you want to connect with main scene, so on ready function, do like this:
your_signal.connect(get_parent().your_function) #or get_tree().current_scene
# when player entered the door emit, your signal
If you are spawning the room by codes of main scene, then you can simply connect them, like this:
new_room.your_signal.connect(your_function) # after add_child