With a "set" trigger, you can just pull one trigger (hard) -OR- pull the "setting" triiger, which drops the pull of the OTHER trigger to just a pound or two. When not properly adjusted, does not work.
Depending in size of buggered screw, you can drill, and use an Easy Out (coarse threaded left hand screw)
Be careul- buggered screw slots are a sign that Bubba has been there. Look for indications of other problems as well.
What we have here is... failure- to communicate.