If of the usual type with a frame on the outside that is bedded on a
sealant like Sikaflex 291 rather than an
adhesive, get the screws out then if one makes up some shallow angle plastic wedges (not too hard so will not scratch the gel coat/paint eg kitchen cutting board polyethylene) and if you can get them going in the edge of the trim gently tap them in. If a proper
sealant has been used and done properly there should be a slight thickness of sealant between the back of the trim and the
boat to start working the wedges into.
With some perseverance this will often just pop the trim off.