here is one way: https://www.hometalk.com/31195184/cheap-easy-homemade-ant-spray
I would pour boiling water into the ant hills. Kills instantly, is environmentally safe and costs nothing.
Here's another simple ant spray using essential oils
Hi Gail - Those little buggers are relentless, aren't they?!? This is the most effective method and all-natural spray DIY that we use with ants. It's best indoors, but will also work outside with more frequent applications. Hope this helps! Hugs, Holly