Once grass dies, there's no hope for resurrection. You need to reseed the patch to make it match the surrounding lawn. To grow grass in a patch, you have to take the same steps you would when growing a full lawn. Preparing the ground is essential or the grass seed will not germinate properly. Even though grass has grown in those spots before, you should still fertilize it and add nutrients to make sure the new grass grows as well as possible.
Prepare the grass patch for reseeding. Seed needs to touch soil directly or it will not germinate. Get rid of anything (weeds, sticks, stones) that would prevent direct contact.
Till at least the top 4 inches of dirt. Loosen it so there are air pockets under the surface. Grass needs air pockets for root spread and development.
Cover the patches with sand and compost. Put down 1 inch of each. This will increase the soil fertility. Till both substances into the ground to thoroughly combine.
Spread a fertilizer that has a high content of phosphorus with a broadcast spreader. Use the package to determine how much to apply per square foot.
Fill a hand spreader with the seed, if you're seeding a small patch. Use a mechanical spreader for larger patches. The seed bag will indicate how much to use.
Rake the seed gently to cover it with 1/8 inch of dirt. This will keep it in place and encourage germination.
Deeply water the grass patch for five to 10 minutes at least twice a day for the first 10 days. After that, the seed should start sprouting. Reduce watering to once a day for 15 to 30 minutes.