Ok, so you need to take apart the gun, simply remove the screws and pry it open, you want to remove the stock and be carefully of the top as it is wired, remove the wiring on the top half of the gun carefully (positive battery connector) then look to the right of the gun and find the switch you are having troubles with, try to get a hot glue gun and carefully melt some plastic around the trigger/button, then remove the button/trigger, give the plastic part a good thorough clean then put it back carefully make sure you don't damage anything else, replace the covers for the switches if there are any, then put back the positive battery connector on the top half. Put back stock. Put halfs together do not screw together yet, test without screwing together, if it works then screw back together, if not reply to this and I will answer.
P.S. make sure you pry open the 2 halves of the gun when the screw side is on top. Don't open it upside down(not a good thing to do)