The correct way is to cut it, it's what's known as a "stretch to fit" belt that doesn't have the need for a tensioner. They are not supposed to be reused.
Dude, those belts are the oddball "stretch to fit" style and are not intended to be reusable, it MUST be replaced with a new one...if you attempt to reuse the old belt it will not have the proper belt tension and may cause slippage on the water pump pulley which can lead to overheating. Just cut the dang belt and then reinstall the new "stretch to fit" one.
