Hi there chicobrew! If you refer to page 18 of the book, it explains the dice pool, and how adding or losing dice from your dice pool works. In summary:
- If a prompt or rule instructs you to lose a dice, you take that dice from your pool of available dice, and set it aside. In this specific case, it means you must select one of any of the dice still in your pool to be removed. Hope that clears things up!