First try pulling it with a good
VESSEL impact driver. I've gotten around a lot of ham-fisted rider stripped screws (many of my own doing) over the last 45 years with one.
If that's not available use a fine tip center punch to mark the center as close as possible and drill it with the tiniest drill you can. Once you have a clean hole increase the drill size a little at a time till you weaken the body of the screw and can peal it out.
If you are very good with a TIG welder, just drop a bead on the top of the screw and let the metal contraction shrink the screw. Done correctly they will usually come out by hand. If the first dab doesn't do it add a bit more till it eases out or you build up enough metal to file a slot in it and unscrew it.