When you cancel an order, the order is deleted, and the queue moves to the next customer. If you just want to remove all items in the customer’s order and start again, you can clear the order. In this case, the customer does not advance, and you can add items to their order.

To cancel the order, click the red X, and then click Cancel Order. 

Notice the next customer is active.

To clear the order, click any item in the order, and then click Clear Order.

Notice the current customer is still active and you can add new items to their order.