When the extraterrestrials go back to alter the past in order to change the future in ways more to their liking, are they riding a new time loop to get there or an existing loop that is ever moving back and forth? Or once back in time, when they change something, is that when a new time loop starts in parallel to the previous past already on record?

If you think about this logically, it must be the case that time travel of the extraterrestrials to move backwards in time must be along a time conveyance of some sort. Otherwise, they would cease to exist at one time point and then reappear at a prior time point and that cannot happen. So this is a looping in a complete sense, as with a circle or ellipse. They traverse time from whatever starting point they choose, and travel back in time to a point they wish to do their tinkering. And once they arrive, they are continuing that loop by redirecting it forward in time once again, and whatever becomes changed goes on record and will eventually supersede what has been going on at the starting point of their time travel excursion. This involves a convergence of the timelines so that the new loop going back into the future replaces what had been the original timeline at the point of departure.