I have some rattling noise coming from my rear bumper and have gotten to the point of getting the tail light assembly out to see the plastic clips. The clips are loose but I can't figure out how to tighten. They have a phillips head and I've tried holding the receiving part with pliers and tightening the top with a screw driver, but that doesn't seem to be working. Does anyone have any tips? Any help is much appreciated. Thanks.

-Austin