My technique for that was to let them out for about and hour or two, before dusk, and supervising them. I did that for a few days extending the time. But I always herded them back into the coop at the same time - dusk - so they continued with the idea that the coop is where they roost for the night. Guineas are creatures of routine, and where they roost is important to them on an instinctive level. Using that will help you
It's a good idea in the beginning to learn to use herding sticks. They work if you use them properly - disasters if you don't. Couple of rules: 1) Never, ever touch the guineas with the sticks. Scares them silly and they scatter, which is not the point. 2) the more slowly you move around guineas with the herding sticks, the better off you are. Otherwise it scares them silly and they scatter, which is not the point. 3) Start with a helper or two until you get the hang of it. Otherwise you end up chasing them with long sticks and you guessed it, it scares them silly and.....
When herding, you don't have to herd all in the group at one time. If there are stragglers, they'll catch up. Concentrate on herding half, or a third of the flock at first.
Herding sticks take about 2 or 3 sessions for the human to learn to use them. They're just extensions of your arms. I use six foot very thin strips of scrap wood, and hold them out in front of me, low to the ground. I move very slowly, and never insist on a "straight line" for the guineas. As long as they're moving in the right direction, I'm fine. I try to stay beside or behind them. The time will come sooner rather than later when you'll go out with your sticks and they'll already be in the coop.
If you haven't been using treats as bribes, start now

. When they go to the roost, give them treats and repeat the same sound at the same time. It can be words, like "time for treats", or shaking the feed bucket, a whistle, whatever, just be consistent with it, and all you'll have to do is make the sound and they'll come running. Make sure they're IN the coop before you give the treat. (Personal learning experience. LOL).
Sufficiently "homed" guineas will take about a week to train to come back to the coop at dusk. Good luck!