boat hull plug tricks?
Take 2 of the screws out and replace them 2" long screws of the same thread, snug them into the wood transom.
Now take a large long flat blade screw driver and hold the 2 screws carefully to keep the brass transom fitting from turning.
Now use a wrench on the transom plug and work the large screwdriver and wrench together to turn the brass plug out.
Then remove the 2" long screws and put the 2 original screws back in, shoving some plumber's putty in the 2 holes first.
Plumbers Putty is great for sealing water leaks when you have something to hold it in place.