When you want to hold an order and take another one, tap the "Open Orders" at the top right.
Taking another order
To take another order, tap "Create a new order". It will go back to the Order screen.
To reopen the pending order, tap the "Open Orders" at the top right of the Order screen.
Select the order referred by the order number.
Up to 30 orders can be saved. When you have 30 saved orders, you have to delete one to create a new order.