You should remove the rear fascia, disconnect the sensor harness, remove the sensor from the sensor housing, sand/grind sonic weld plastic residue from the fascia, apply structural adhesive epoxy, Lord Fusor(TM)127EZ or equivalent, to the fascia at the mating surface, install the sensor housing to the fascia, allow adhesive to cure according to manufacturer's directions, install the sensor to the sensor housing, connect the electrical harness and install the rear fascia.