Block them off until they are laying age
They don't need access to them until they are ready to lay, and if they can't get to them, they'll learn to sleep on the roost instead. Try also raising the roosts up. It looks like you have one of the little pre-built coops, so you might have to get creative, but chickens like to sleep as high as they can. Get the roosts higher than the edge of the nesting boxes, and they'll prefer to sleep there. Maybe take out those pre-built roosts and put one long one in running the other way up high, and they'll want to sleep there.
Unfortunately those coops oftentimes are designed to look cute to us but are not built with practicality and real chickens in mind. They also often say they will hold far more birds than they really will. How many birds do you have? You'll probably find yourself upgrading to a different coop in the future - that's usually what happens, unfortunately.
Edit: In your avatar I see six chicks. If you kept all those, and that's the coop I think it is from Tractor Supply, it's going to be way too small for your girls. You may want to just build a new, properly sized coop and scrap the idea of using yours. Maybe put in on craigslist and build something better suited