“wpcargo_tracking_number” is the default shipment field name attribute.

To change the track form name attribute, copy and paste this code to your theme functions.php file

add_filter('wpcargo_track_meta', function(){
        // cargo_meta - is a sample track field name attribute. You can change any name you want.
	return 'cargo_meta';
});

Note: This filter hook is available only in WPCargo 6.9.1 version

To add the updated track form name attribute to email, copy and paste this code to your theme functions.php file

add_filter( 'wpc_email_meta_tags', 'custom_additional_email_meta_tags' );
function custom_additional_email_meta_tags( $tags ){
    $tags['{cargo_meta}'] = 'Tracking Number';
    return $tags;
}