If ever you need to transfer or combine a guest's gift card balance, the best way to do so is by using the Transfer Gift Card tool.
In Toast Web, navigate to Payments > Gift Cards > Transfer gift cards.
Note: You will need the old card number and the new card # before moving to the next step. You can find the customer's account by navigating to Reports > Payments > Gift Card Transactions.
You will have two options once you select Transfer gift cards.
Transfer the balance of card A to card B. Deactivate card A (transfers the old card's balance and deactivates so that it is no longer valid).
Combine card A and card B. Both card/account numbers will represent a single, unified cash or points balance (leaving both cards active but sharing the same combined balance).
Choose which action you would like to take and then select Next. You have successfully transferred a gift card account!