Certified GKH Gardening Expert
I would try, first, to reseed the lawn. If that does not solve the problem, then you will want to treat the lawn with, both, DOLOMITIC LIME and WETTABLE SULFUR. These two will kill off infections in your lawn, as well as recondition the pH and provide several micro and trace nutrients back to the soil.
This article will offer ways to prevent future issues with the lawn, and to repair brown spots: https://www.gardeningknowhow.com/lawn-care/lgen/brown-lawn-fixes.htm