When I bought my car, the rear bumper was resting on the tailpipe......
Anyway, Open your trunk and below your tail lights, and behind the carpet, you should see the bolts that hold your bumper in place. There are 2 bolts per side. Mine only had one on each side. You don't necesarily need OEM bolts. Just get you some that would fit through the hole and long enough to tighten down. It takes 2 people to perform this task because if you use different bolts, somebody has to hold the other one with a wrench or crescent wrench or ratchet to keep it from spinning. You should be able to see the bolt from under the bumper as well. It is probably better to remove the bumper and make sure that the guides are in place. It's not hard to do. 20 mins tops. Good Luck!