Offload disambiguating to the shopping cart with a fast, in-line interface that enables the customers to quickly correct or choose alternate products.
This builds on the existing mental model that users have for using the cart as a list and helps offset some of the lack of precision of voice, to help build confidence and trust.
(Future: There is also an opportunity to extend the swap functionality universally to all items in the cart (i.e. solve for OOS a.k.a. Out Of Stock, etc.))