To sort readings alphabetically by title or author:
click the ellipsis menu at the list level.
click 'Order citations in all sections'
choose how you would like items to be ordered (e.g. by title, by author, ascending or descending)
a pop up window appears asking you to confirm the action. You can't reverse this action but you can continue to move items around manually. Note: items will remain in their sections and only reordered within sections.