Well if they are used to the coop, they should return to it when dark gets close as it is a place they consider home, or at least safe. A light on would help. I had to pick mine up and toss them thru the door one at a time the first day, but they had never been in the coop before. The second day most went on their own. Some still don't like to go in, a year later. One of them earned herself the name 'Stupid' because she would always try to sleep in our gazebo and now that we've moved, I think she is searching for it!
But even she goes in now, even ranging a whole acre. Coop is safe, coop has food. Most will simply do it because it makes sense.