Need help on 1990 q45

Hello,
I would appreciate it if you can help me with the following.
I'm trying to change both sun visors on my 1990 Q45.  The visors have
lights and come with cables that has to be routed under the big plastic
piece on the ceiling.  My question is how do you dis-assemble the big
plastic piece?  Where are the screws or snap features that are holding
it in place?

Thanks for your time.
Ray