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.