Crab grass is, in our area of the world, a hot weather annual and the plants now growing will die when the weather turns colder. These plants do produce large quantities of seed that can germinate next year, give half a chance. Since Corn Gluten Meal is a pre emergent control the time to apply that is in the spring about 6 weeks before the crab grass seeds will be germinating, applying any pre emergent now to control something that is already growing is largely a waste of your time, energy, and money.
CGM is also known to be a good source of Nitrogen, however, so if you want to use it for that now you could, an expensive source of N however.
Grasses grow best in a good, healthy soil and the only way you can know what your soil is like is with a good, reliable soil test. Have you had one done on the lawn in the last 5 years?

Corn gluten inhibits seed germination. If you use it and overseed, you are killing the seeds you just spread.

Next spring, apply it before the weeds start sprouting.

Thank you for writing before you did anything. These comments will save you a lot of time.

Don't use corn gluten meal on established crabgrass. It will only fertilize it. As was said, corn gluten meal is only recognized as a PRE-EMERGENT weed seed controller. If you want to use a pre emergent, then use it in the spring when you are not reseeding.

Crabgrass will die by itself. You don't have to do anything. If you want to over seed or reseed, and if you have crabgrass you probably do, then you should get rid of the established crabgrass before seeding. I would probably use a power rake and take it all the way down to the soil. Then reseed. Be careful with the power rake around your sprinklers. Put flags up or something to warn you where they are.

Also DO NOT bring in any new soil unless you have low spots you want to raise. Chances are your soil is already higher than the surrounding concrete which indicates you do not need to add more.

Having that much crabgrass in the lawn indicates several things. First of all your grass is not dense enough to shade out the crabgrass. Crabgrass can only survive in full sun. If you have dense, tall grass, it will never get started. The other thing it indicates is that you are getting water too frequently. If you are watering more often than once a week, that is too frequent. Crabgrass seed needs frequent watering to germinate. So with this in mind, first of all you need to seed in as much grass as it takes to cover the lawn completely. Kentucky bluegrass is great because it seldom needs to be reseeded. It spreads to fill in bare spots. After you get the grass established, make sure you don't water too often. This means you'll have to water deeper (longer) each time you water. Then reset your mower to the highest setting. Tall grass will look much better and will keep out almost all the weeds.

Thank you everyone for all the very good advice. I am going to get a soil test, try to pull up as much crabgrass as possible and seed. Unfortuntely, my sprinkler system for my lawn and my vegetable garden are on the same zone, so the lawn is definitely getting watered too frequently. I will also look into the cost of separating the zones. I know that maintaining a healthy lawn is the best way to keep out weeds without any chemicals (which I won't use), I just needed advice on how to get the healthy lawn!