If it's a small area just replace the topsoil by buying a few bags of topsoil for Lowes, etc. Jusst add grass seed, cover a little and water a lot in a few short days a happy area appears.
You may just want to add some topsoil to the area or even breaking it all up with a rake, hoe, etc.
I have spots all over the place in my yard that I've been patching the past year or so. A couple were nothing more than fill dirt used to level the yard where we had some septic tank/line work done. I've dided all of the above and more.
A couple stubborn spots I bought bags of Scotts Patch ? to give the areas a boost, ask me next week on how it's doing.