Make sure the unit is face down on top of some sort of soft surface that completely supports the entire screen from side to side and top to bottom. 

2nd, it's quite possible that the fitting has fallen behind one of the address boards at the bottom, if it has, do not attempt to remove these to get to it, there are ribbon cables attached to it which can be torn easily.  Tear and ribbon cable and you've ruined the PDP panel..  not covered by warranty.  Very, very expensive.

3rd, even if you get the fitting out, which you should to prevent any potential short circuits in the future, you can't just reattach it to the frame.  We've had a few of those inserts fall out and were forced to order the metal frame piece from Philips.  This is an issue they are aware of.  You'd really be better off letting an authorized service center deal with this.