I don't have ramps but I've seen folks suggest using treats to lure them up and down, or if the birds don't mind being herded (aka they don't run away at the sight of you) you can gently herd them up with a couple of sticks.
When you do let them out, you may still need to train them to use the ramp to get in and out as it seems chickens don't really instinctively know how to use them.
Doesn't hurt to leave them in coop only for a few days, provided that there's plenty of space, ventilation, and natural light, to help home them to the coop.