Replace it. There's two threaded brass inserts for the bolts that hold it on. Those inserts have broken out.
You might also try gluing them in place with epoxy. To insure the glue sticks, wash the plastic first with soapy water to remove any remaining mold-release chemical. That's the oil the lets the handle pop out of the mold without sticking to it. Rough it up with sandpaper to remove the shiny surface.