Lawn weed identification
I assume that you sent a photo but it didn't come through could you try again?
It is Prostrate Knotweed. It can be pretty aggressive. It sounds like you may need to start over if you don't have any grass growing. Now is not a good time but once it cools down in late Aug. would be better. Here are a couple of links to info about it as well as how to renovate your lawn. https://apps.extension.umn.edu/garden/diagnose/weed/idlist.html#PKnotweed . https://extension.umn.edu/lawns-and-landscapes/lawn-care