GCP-
If your bike is like mine (2011 B5), that metal cover is part of the spark plug boot. The top of the plug has the small threaded metal spindle exposed (when I replaced my OEM Bosch plug with the NGK, I had to unscrew and discard the smooth "hourglass"-formed adapter piece that came mounted on top of the new plug), and that metal cap slides on and grips the threads. I just reach in, grip the metal cap, and pull it off. You can hear and feel whatever grips that threaded spindle "dragging" on the threads as you remove the boot.