When you first moved them from their brooder into the coop, did you acclimate them by closing them in for at least one entire day and night? Or did you just toss them out into the run and expect them to go into the coop when night came?
If you haven't followed the protocol of acclimating them to their new home, then what you need to do is let them spend a day or two locked inside the coop. This should give them the sense that this is where they will be safe at night, and awaken the instinct in them to return to it each night at dusk.
If you did follow this protocol and the chicks just aren't taking to the coop, you might find it beneficial to repeat it.
Going into the coop at night is instinctual, and you just need to get it cooking.
If you haven't followed the protocol of acclimating them to their new home, then what you need to do is let them spend a day or two locked inside the coop. This should give them the sense that this is where they will be safe at night, and awaken the instinct in them to return to it each night at dusk.
If you did follow this protocol and the chicks just aren't taking to the coop, you might find it beneficial to repeat it.
Going into the coop at night is instinctual, and you just need to get it cooking.