Hi Lynn, here's a site with info all about crabgrass and getting rid of it. http://www.garden-counselor-lawn-care.com/getting-rid-of-crab-grass.html
Any chemicals that kill Crabgrass WILL kill your lawn grass also - they are in the same "family". Best choker is a thick lawn that you allow to be mowed on High level only, so it remains taller, thicker and kills off the crabgrass.
This post will help. https://www.epicgardening.com/crabgrass/