When following the Carry Over plan and searching the database any relevant free foods to your search will be displayed at the top of the search in green with normal calculated results below.
You can either choose one of the free green ones or alternatively choose any other entry and then use the free food switch before adding to the diary to turn it into a free food.
It is unfortunately not feasible for us to change every item in our food database but we always ensure free items appear at the top.