Answer: If the weeds do not respond to weed killers, dig them out, roots and all, then over-seed the lawn, including the bare spots where you've removed the weeds. The new grass will germinate in 7-10 days and will help thicken and green up the lawn. Or, you can use a weed and feed product, wait 3 weeks and then overseed the entire lawn. It should green up quickly.
Best wishes with your lawn!
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