Certified GKH Gardening Expert
You can check with your local extension office for help with locating someone specializing in lawn care. They may also be able to provide advice themseleves. A soil test can be helpful as well.
In most cases, dying grass is caused by a lawn fungus. Here are some of the most common: https://www.gardeningknowhow.com/lawn-care/lgen/grass-fungus.htm