The Pacifica wheel has 4 belts that all need to be there in order to run properly. I would assume that there may only be one belt left. take the bottom cover off and see what is there. You need to take the one belt off and measure because there are two different sizes of belts for reorder.
If it just an adjustment that is simple on that wheel, there is a plate that the motor is mounted to that has two threaded rods with adjustment nuts.