Rake up as much dead grass as possible. This will allow the gypsum to come into full contact with the soil.
Fill the hopper of a lawn spreader with granulated gypsum. Set the spreader so it will distribute 40 pounds per 1,000 square feet of lawn.
Walk the lawn with the seed spreader. Walk in parallel laps so you do not miss any spots.
Water the gypsum into the soil until it dissolves. Use a regular garden hose. The gypsum will remove the salt molecules in the soil and replace them with harmless calcium.
Cover any bare areas with a 2-inch layer of mulch. This will keep down weeds so you can reseed the spot in the spring with grass seed.