WARNING: This page is about a different car, the 2009 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
Remove the plastic nut (A) of the reflex reflector from the backside of the bumper.
Press the tabs (B) to remove the reflex reflector.
Fig 1: Identifying Reflex Reflector Plastic Nut And Tabs