Rear lights and broken clip

[pmmcbl]

Hello guys I need your help.
I had to replace both outer rear lights on my 2009 Passat estate. Job was easy to complete but I managed to break something! There is a washer/nut which is made of plastic which its job is to keep the light secured and in place.

Well I managed to turn it a step to far and broke the part where the nut was turning into. So I assume I can get the part plus another washer/nut. But how easy is it to replace? Do I need to remove any interior trim?

Thank you in advance