In order to automatically receive tracking numbers from Zendrop to your WooCommerce store when an order is marked as shipped, you will need to first make sure sure that your WooCommerce store is connected to your Zendrop account (click here for more information on how to accomplish this). Once that's done, head over to your WordPress account, and click on Plugins.
You'll want to download a plugin called Advanced Shipment Tracking for WooCommerce. Once you're on the Plugins page, click Add New at the top.
Search for Advanced Shipment Tracking for WooCommerce using the search bar, and click Install Now.
Once installed, the final step would be to click Activate.
Give it some time to activate then that's it! As soon as an order is marked as shipped on Zendrop's end, the tracking number will be sent to your WooCommerce store without requiring any manual work.