This article got me thinking If NASA is going to use our primitive space exploration technology to capture an asteroid wouldn't an Extra Terrestrial species have used UFO's to maneuver celestial bodies? They clearly would have come across this problem along time ago and the videos of UFO's levitating and vectoring themselves demonstrates they operate on similar applied electromagnetic forces that the celestial bodies use to maneuver themselves around in solar systems. Couldn't they maneuver meteors, asteroids, possibly even speed the advance of collisions developing protoplanets and move moons into orbits with planets? Maybe they build solar systems to live in they way earthlings build housing developments?
You are assuming
Asking what they would do if they existed and if they had capabilities is really the realm of science fiction. There can be no good answer to your question at this time. Maybe later we'll know, maybe never.
One of a million possible answers:
An advanced civilization wouldn't do this without need. If necessary, they would use gravity instead of magnetism, since magnetism acts differently on different kind of matter, gravity is much better suited.
They would know the need long time in advance, hence be able to act, when there is still enough time to get the desired result with a reasonably small effort.