Pull the outboard side of the lamp rearward far enough to disengage the two ball studs on the back of the lamp housing from the plastic grommets in the lamp opening of the body sheet metal.

This will create a gap between the body and the lamp.

Locate and remove the plastic push-pin fastener that secures the bracket on the bottom of the inboard side of the outer rear tail lamp housing to the upper flange of the rear fascia. Use a thin tool for some gentle prying if the pins are a little hard to remove.