The fasteners push in the rear pannel and then the thread on the number plate pannel push into them the number plate screw plugs also help hold it on .
You will need to lever the captive part of the fastener appart to remove them
You will need four new captive fasteners to refit it,I woud use a small amount of sealer round them on reassembly as they are very prone to letting water in.
Cheers Tim.