How would you correct a rear bumper molding that has come loose and is hanging down?

Try some 3M structural adhesive. Should be ava. at good hardware store or parts dept. of any GM dealer. Two (2) part epoxy. Apply to both surfaces hold in place with Duct Tape, sets in 2-5min. Color cream... The main thing on these bumpers are they have a circular disk that fits in a slot. Hard to get it in, but when you do, take a regular metal screw and install in the lip of the metal fender well..Very common problem on these cars..