It's very simple--2,4,d.
It comes in liquid or granular, usually in fertilizer sold as "weed and feed." If you buy this be sure to only use it while the grass is wet (NOT during a rain). Early when the dew is on is good, or you can spray it with a hose.
If you want cheaper stuff go to a farm supply store and get a gallon of the "amine" type for about $20 and mix it yourself--usually 2 oz. per gallon of water--and spray it with a backpack sprayer. I do it at night when there is no wind.
Keep in mind it will kill any/all broadleaf plants (no grass!), so that means flowers, small trees, and other things you may not wish to kill. You can avoid them easily with a backpack sprayer, but if using a broadcast spread you will need to cover them--tarp or black garbage bags. Or you can get an assistant to simply hold up a sheet of cardboard or plywood to block the granules.
You will see shriveling in 24 hours.