Dum brake light question

[mark-tda4s]

OK, I am no rocket scientist but not a dummy either but how do I remove my brake light bulb on my 97 Chimaera with the later cluster?

Looking from inside the boot I thought it would be a simple matter of pulling the rubber cover to expose the bulb but it doesn't budge. There are no screws and the larger steel boss appears to be bonded to the fiberglass.

Any help appreciated!