For three years, my three hens have reliably laid their eggs in one of our two nest boxes. They never touched the second box, always choosing nest box A. Well, a few days ago, one of our chickens decided that she wanted to sleep in the nest box. As a result, after three years of reliable laying, all three of our hens are laying in the back corner of the coop
What can I do to A: stop our chicken from sleeping/soiling the nest box at night, and B: get them to start laying in the nest again?

What can I do to A: stop our chicken from sleeping/soiling the nest box at night, and B: get them to start laying in the nest again?