Chickens should go in on their own after a few nights. Something is up if they aren't. Either the kennel does not have everything they need such as suitable roosts and safety or it's not dark enough out yet. Sunset is now 8 20 here and mine don't put themselves up until 7 30 to 8 pm but they always do it. If I tried to get them at 6 30 I'd have to spend 30 mins rounding them up when if I just waited they'd be up by themselves another half hour later. Are your chickens trying to roost elsewhere or are they still wandering the yard when you try to get them?
I have never trained chickens to go to Roost we just go out and shut them up after dark. They always figure it out. Every now and then one misses the curfew and I find them out in front of the door walking around the next day looking for their gal-pals ( they don't usually repeat this behavior)