Use the tool pictured above along with a heat source to warm the butyl sealer. A very hot summer day is ideal, but a heat gun will work also.
Heat the trim piece evenly along its length until very warm to the touch, maintain this temperature for 5-10 minutes to allow the butyl sealer to absorb the heat and become soft. Most times lower w/s trim needs to be removed this way to prevent bending and damage.
Extra time and patience spent here will prevent/offset time and effort spent on trying to straigten bent pieces.
Hope this helps.