My Rotom possessed its own Pokéball and can’t come out??? The Pokéball thinks it’s simultaneously inside and outside???

Press and hold the front button until you hear a pop. This is a safe factory reset for poké balls that fail to work properly. Once you hear the pop, immediately let go of the bottom of the ball (while holding the top, of course), as the ball will immediately eject any pokémon inside, including part of your rotom. Normally, the next step is to use the newly reset ball to recapture your pokémon (unless you’d rather not risk it, which is perfectly understandable), but in your case, you’ll want to set the opened ball on the ground or a solid surface and have your rotom come out. Now that the ball doesn’t recognize the link between itself and your rotom, this will give your rotom a window of opportunity to escape. This should be done quickly, as the ball may snap close and catch your rotom again.

The alternative is, of course, taking a hammer to the ball. (This won’t hurt your rotom, as it’s in an incorporeal form. It will only force your rotom to eject.) But of course, this destroys your rotom’s ball, so it depends on whether or not you’d like to buy a new poké ball for it.