Click Refund on the saved meal row (confirm "Are you sure?"). The meal is voided (struck through) and, because the slot is now free, an Add <category> button appears on that row; use it to pick the new meal and Complete Checkout. For an included meal no money moves (the model only issues a refund when the meal's charged amount is greater than $0). This works only while the day's status is Open — the Add button doesn't check whether the delivery date has already closed for ordering, so in practice you can still do this after cutoff, but you should coordinate with the kitchen because production lists are already generated by then.