So when a new threat comes to Earth, new heroes can come in and fight the forces of evil, and there’s no shortage of established power sets you can give them, though I’m inclined to go with Zeo since the Zeo Crystal is already established.
Take advantage of the time gap between the two movies by having the original heroes having all left the Ranger life behind long ago.
Throw in the fact that there have been so many Power Rangers team-ups over the years, and you can easily introduce a new team of Rangers who exists in this film continuity rather than having them exist in yet another separate universe.