little ribbon guard mainboard

hi

I just reassembled an new display on my iphone 4 and unfortunately this little black ribbon guard on the top of the mainboard broke off(or is not inserted anymore)

Note that there is a rubber guard on the edge of the logic board where the Digitizer and LCD ribbon cables bend over the logic board. Make certain it is there before replacing the logic board during reassembly.

can anybody tell me, where this piece has to be inserted??or what it is actually for??

thanks