Add tracking numbers to fulfilled orders
To add a tracking number to an order that has already been fulfilled:
From your Shopify admin, go to Orders.
Click the order number for the order you want to add a tracking number to.
In the Fulfilled section, click Add tracking:
In the Edit tracking dialog, enter your shipment's Tracking number.
Shopify might recognize the tracking number format and choose a shipping carrier for you. If it doesn't, or if it chooses incorrectly, then choose your shipping carrier from the Carrier drop-down menu.
If your carrier isn't fully supported by Shopify, or if you select Other from the Carrier drop-down menu, then you can enter the Tracking URL manually: This tracking number will appear on the order status page. Make sure that you enter the complete URL (including the digits) that your carrier provided to track the shipment.
Click Save to confirm your changes.