Help with st Augustine lawn

So I just bought a house and have inherited a lawn that’s not in great shape. I’ve hired a lawn company to treat a couple of times a year but I find them very demeaning when I ask how to resolve specific spots in the lawn.

I’m assuming this is under watering? But I’m a bit confused why some of the grass around it looks to be healthy.

Any help is appreciated! I’m a little overwhelmed trying to take care of a lawn for the first time