Patience is your friend here.
I’ve always been successful by wetting each screw remnant liberally with penetrating oil and giving it plenty on time to soak. As best you can, find and punch the center of the screw and begin drilling with as small a drill bit as you can. Then drill repeatedly by increasing the size of the bit each time.
Most often, a screw extractor bit can be used to back out the screw remnant. If not, drill out until you can use the correct thread tap to excavate the remaining remnants of the screw from the original threads.
Of course, there innumerable YouTube videos which detail other ways and variations on the steps I outlined above.
Good luck!
Greg
