Ok so no fret here if you accidentally pull off the metal insert placed on top of the actual antenna. This step needs to be rewritten imo, the deal here is that there is an actual 'socket' looking deal underneath here that you need to lift up. There is a metal tab semi'glued' to that part of the antenna and it does come off easily, however all you need to do is press them back together to get them back, I believe it to be a range 'extender' of sorts.
So your looking to actually lift up what looks a lot like a ribbon cable as well in this step. YOU SHOULD NOT HAVE A PIECE REMOVED IN THIS STEP, it's still in the case at this point.