Normally we replace the entire tub waste if it is that corroded.
You can try drilling out the old screw very carefully and retapping the new opening with the next size larger tap. Or you get what they call a large cock hole cover (a crome plated cover) and attact it to the existing over flow tube and buy a rubber stopper for the
outlet.
The cockhole cover for the tub can either be a flat plate type OR the better one is the one with the over flow provisions.
Good luck