If you're talking about the whole c pillar trim, you need to pop off the small plastic "airbag" cover. It is a retaining clip for the whole C-pillar trim. I needed to use a small trim removal tool, a plastic screwdriver could also work, to shimmy it out. Once that plastic cover is off, the c-pillar pops off at the top. I only need to get that far as I was doing a dash cam install and just needed to tuck cables in.
The bottom half may or may not be more involved. not sure if the lower trim in the trunk area needs to be released.
