You could instance the same scene again, add it to your games root-node (
get_tree().get_root() or just
get_parent() in root-node of your scene)
then set it to the desired position, move your player into the new room, and queue_free the old one.
Or just hide it (
visible = false) it, incase you want to go back. If your Roomgenerator is deterministic, you can just save the seed from the random number generator and regenerate if, if nececcary.