Complex sentence: Abigail is able to reverse the spell, if the elevator is repaired-as long as the team finds something that belonged to each of the hotel guests, and repeat their actions in the elevator on Halloween, freeing their spirits from the hotel.
Split into simpler sentences: Abigail is able to reverse the spell, if the elevator is repaired. She can cast a spell if the team finds something that belonged to each of the hotel guests, and repeat their actions in the elevator on Halloween, freeing their spirits from the hotel.