Preheat oven to 350 degrees. Cut or pull apart chicken and place in the bottom of a 9 x 13 casserole pan. In a bowl mix the soup, milk, cheese, and mayonnaise. Pour soup mixture over the chicken. Mix butter and Ritz in bowl. Spread Ritz over the top of soup mixture. Bake for 15-20 minutes or until soup mixture is bubbling and crackers are golden brown.