This is a great documentation of Brown Patch, a very common fungal disease of turfgrass in summer. You can learn about it on our Diseases of Home Lawns page, which includes general management tips (mostly related to prevention, as fungicides cannot cure existing outbreaks). Affected lawns usually recover on their own without intervention, when growth resumes in early autumn. (We presume this is a tall fescue lawn, not zoysia?)

If you did decide to try a fungicide (which we don't recommend for reasons listed on that page), it should be applied by a certified pesticide applicator, which most lawn companies have on staff. Be aware that, depending on weather patterns and other environmental factors, a fungicide treatment regimen won't always work completely to stop a disease from spreading, and fungicide treatments may be more costly in the end than simply overseeding the lawn in autumn to fill-in any sparse or weak areas, which is a recommended practice even for healthy lawns.

Miri