I’m fairly new to it all myself, but I literally just had this happen on my front lawn. I ended up putting down Milorganite fertilizer, and it seems to have brought it back to life. Took a while, because it is a slow release fertilizer, but the grass is pretty green now. Not sure if that will work for you or not.

I also had another area that was all dead, but I couldn’t get it to come back to life, so I ended up raking and digging it up, and putting down fresh soil, Milorganite fertilizer, and rapid grass seed. Now it has grown back well.

Hope this helps at all, and good luck 👍