Soak in AeroKroil for a few hours but be careful with leaving it set puddled on external finish too long (over night), It will remove blueing. Kroil has been a miracle worker for me many times. Prying will break the stud and then it’s really gunsmith time. Maybe slip feeler gauges between trigger and frame to help with upward pressure. As a last resort I would try a little heat on the trigger with either a soldering iron or a small butane torch. Good luck!