Hey Sarah
One thing i always do, is giving my chickens a bowl of water with ice and frozen berries (mostly if they dont drink enough, but also simply because they love to catch the berries lol). Also try to keep their feet cool, either with shallow baths, or (if they dont like water) cold bricks in the bath, so your chickens can stand on top of those (the bricks usually soak up the cold water and, therefore, get colder pretty fast.
Or, if you can, put sand in the Fridge overnight and give it to your flock to "bathe" in.
The thing that worked best for us, is actually also the easiest. You probably have trees or/and bushes in your yard/where your chickens are. Try to wet those with a hose, almost like watering plants. Idk exactly why, but it gets so much cooler underneath if you do this

same goes for big wooden crates with like a cold towel on top. Youd just have to cut out a hole on the side for your chickens to get in. (I hope my terrible explanation is somewhat understandable)
I hope my tips help a little and good luck with your little friends trough those hot days!