To delete a sent dish, mark it in the order and select Delete in the list of operations.
In the next window, choose the reason for deletion and click on Delete.
The dish will be removed from the order.
To delete multiple dishes for the same reason at once, select all the desired ones in your order and repeat the procedure.
You cannot delete both sent and unsent dishes simultaneously. A warning will appear when you try to delete them. Swipe it off the screen and then delete the sent ones first, followed by the unsent ones. Or vice versa.