Just like farmers who depend on chemicals to grow crops, any use of chemicals on your lawn has killed the life in your soil.
I agree adding chicken compost as an option, but you have to keep this practice up for years until your soil has come back to some life. Conventional farmers are finding this "transitioning" soil to take 5-7 years.
There are some short cuts to bring back life to the soil, I think I saw one here which we did for years- mix
mushroom spores with liquid, somewhere here they recommended a light oil, and that will bring in some life so the rest of the microbes can take hold.
Other ways people add microbes- fish emulsion, manure, compost, with no one being better than the other, but doing all of them certainly can't hurt.
We use NoMowGrass as our lawn and it uses no chemicals to thrive, it also only needs a seasonal mowing and it is a soft, cool grass. It makes The transition easier.