Mike wrote:

You can use a 2-4-D product such as Killex to kill all the broad leaf weeds
in your lawn, it wont harm the grass.

As long as you don't put it down when it's 85+ or the grass is already
stressed from lack of water. Most weeds should have been dealt with
earlier, like June, when temps were more moderate. If you work on this
for a couple years, properly fertilize, seed if needed, etc, the lawn
should not be full of weeds anymore. All that should be required is an
occasional spot treatment with a sprayer of weeds.