I had to do the same thing with my LK rifles. I used brake cleaner. Put the little red straw on the nozzle, be sure to wear eye protection. Go outside and hold that out. Put the red straw inside the trigger assemble itself. And start spraying. Spray generous amounts. And get into every little hole and opening.

I even once took the trigger and tied it on a string. I put it is VERY HOT soapy water and kept dunking it up and down. This was to get any oil traces or grease traces out of the trigger. When the trigger cooled I then took it outside and sprayed it down with brake cleaner again. Then just a drop or two of oil, when you're sure the trigger is clean.