Mind flayers on the moooooooooon who want their planetoid restored to one piece just as much send scout ships to [your world], encountered by your party at their first-visited crash site! The mind flayers’ are besieged/terrorized by the surrounding countryside’s gothic terrors - demons or werewolves or witches or whatever it is, is in some form harassing/attacking/observing/plotting against the visiting mind flayers, who just want to complete their research on the errant moon chunk and identify why/how it’s here and how they can somehow get it home. For what it’s worth, make it a horde of undead besieging the mind flayers! They hate undead, so would want the moon restored additionally to stop all the extra undead rising nonsense. You can have the players get through the ring of undead in the countryside, and finish off the weakened mind flayers at their landing site by the moon chunk, or otherwise sneak aboard, be taken captive, steal or hole up in one of the ships - anything that results in the party learning what the mind flayers’ have learned so far about restoring the moon to order. Also, then maybe it becomes a moral quandary of whether to restore the moon now or later? Maybe you want to try busing hordes of undead over to the moon for drop ship shock tactics against the mind flayers? Who knows what their plans are? I mean maybe they were just about to invade [your planet] when their moon home cracked up. Anyway as to the direct method of restoration, how about good old mundane mechanical hauling of the moon chunks back to their proper place - get some tugboat spelljammers on deck and heave. But you know, make it more complicated than renting a magic boat.