Not a lot you can do with ants. Brush the soil away, then mow the lawn. There is little available to treat ants in lawns. You are at the worst time of year because they are getting ready to leave the nest and go and form new colonies. You may see flying ants soon, if they've not gone already.
The standard treatment for killing ants is boiling water, but in a lawn this is troublesome. You have to dig up the lawn and get down to the nest and hope that the queen is around. Then pour a kettle of boiling water over her/them. This will kill them, but it is a pain of a job, and stands a chance of killing the lawn as well.
There used to be a treatment available to commercial lawn growers, but like all the good things in life it has now been banned by EU. There is not a lot you can do, sorry.