After you have shipped an order, you have the option to re-ship it again.
Why would you want to do this?
If your customer failed to get the order and you want to send out a replacement.
How do you re-Ship the order?
In the order popup, scroll down to the shipment section and click next the shipping company/service you want to re-ship and click the Re-Ship button, which is a icon of a truck.
What happens once you have re-shipped the order?
This will create a new shipment on this order including creating a brand new shipping label with tracking number for you. This will also re-ship everything that has been allocated to that order.