This will require significant effort. But it pays off quickly. If I can teach five-week olds to go into the coop at night and roost, you can train older ones to do it.
The first step is to put them into the coop as soon as all the hens have finished laying. Ideally, you should put them in at least two hours before dark so they can explore the coop and be comfortable in it when dark comes. Close them in and the adults out.
Second step is to place them on the perch at the opposite end from the adults and reassure them by placing a hand lightly on their backs while on the perch. By the time it gets dark, they should stay on the perch. If not, let them sleep on the floor. Let the adults in after you get the youngsters settled.
Next night, you will need to get into the coop and entice them to come inside. Use a treat to lure them in. This method is not as easy if you are also dealing with adult chickens in the same coop. It helps if you have a coop with two entrances and can partition the coop so the youngsters aren't competing with the adults. I have two coops, one dedicated to teach chicks coop life. It really helps.
A night light in the coop can act as a beacon to draw in the youngsters in at night. You can turn it out after they are settled in. You may need to encourage them inside for up to a week before they are going in on their own.
