Hi, welcome to GoY, as you've used weedkiller, {presumably not a lawn weedkiller, which is designed to just kill broadleaved plants in the lawn,} you will need to wait until the weedkiller has been washed out of the soil, and then resow the bare patches, depending on which weedkiller you've used, it can take up to 6 months to clear, Derek.

Bluegrass, bent, and creeping fescue will grow in from the edges, but possibly not fast enough.