Deep all day shade is best but....
I give a dose of Sav-a-Chick electrolytes/vitamins about once a week during heat waves.
It really seems to help....started this after they saved a heat stroked hen once.
Can mix up a smaller amount, just wrap the packet tight and store in a dry cool place...
You only need one, to put inside the coop to lure them in.
How many birds do you have?
Is there a floor in the upper coop portion of the tractor?
Is the back part of the coop portion solid or meshed?
How many days has it been?
Do they go in and out of coop during the day?
Show us your coop and run?
I've used a battery power puck light to lure young birds inside at night,
turn it on an hour before dusk and turn it off when locking up after dark.
But if it is hot in coop they still may be...