Herbicides kill crabgrass, but if you don't want to apply chemicals to your lawn there are alternatives available. One option is overseeding your lawn to add additional grass so the crabgrass has more competition for resources and can't become established.

Will overseeding choke out crabgrass?

You can overseed into existing grassy weeds like crabgrass and then apply pre-emergent crabgrass killer the following spring to remove crabgrass from your lawn. ... The crabgrass killer will also kill germinating turfgrass seed.

Should I pull crabgrass before overseeding?

No sense trying to kill crabgrass now before overseeding. It'll be hard to do, plus frost will kill it in another few weeks anyway.