With some soapy water. Here is some info to help. https://www.wikihow.com/Kill-Ants-Outside
pour boiling hot water on and around mounds. draw back is it will scorch grass. be careful of carrying containers of hot liquid. do this at about 3 in afternoon when they are most active. hope this help.
Boiling hot water will work, maybe in a tea kettle for carrying safety.