All you can do is apply lawn weedkillers - Verdone is probably the one to use, especially now, when its too late to feed the lawn. Needs mixing up in a watering can and applying. Next year, either use Verdone and a separate feed treatment for the lawn, or buy a combined product in granular form, usually sold as Lawn Weed Feed and Mosskiller or just Lawn weed and feed. These are generally not quite as effective as Verdone at killing weeds though, but the rule is, if you're applying lawn weed treatment, you should also apply a feed for the lawn - in spring and summer, not now.