Print Invoices, Packing List & Labels Plugin for WooCommerce - Add ship date and tracking number to shipping labels. https://www.xadapter.com/product/print-invoices-packing-list-labels-for-woocommerce/

functions.php

add_filter( 'wf_pklist_label_add_additional_information', 'wf_pklist_add_tracking_number', 10 , 1 );
function wf_pklist_add_tracking_number($order_additional_information)
{
	$tracking_number = '78965413301236547893210'; // Change this to desired one.
	$ship_date = '07-08-2016'; // Change it to desired one.
	$order_additional_information['tracking_number'] = $tracking_number;;
	$order_additional_information['ship_date'] = $ship_date;;
	return $order_additional_information;
}