Disco 5 rear brake light

[Thevet]

I have a 2018 disco 5 which has now got a failed brake light on the left, looking at the access to replace, does anyone know firstly if there is a bulb to replace or secondly how to get the light cluster off, I can see one 10mm nut to undo (but it is now just turning ugh) but cannot see or really even feel a possible 2nd fixing. How do you get this fixed?