functions.php

/* this would go in your child theme functions.php: */
function custom_shipping_message () {
	$message = 'your message here';
    echo '<p>'.$message.'</p>';
}

/* this would go where you wish the message to show up in your product-edit.php 
template which you have copied and moved to your child theme 
(wp-content/themes/your-child-theme/wc-vendors/dashbaord/product-edit.php): */

<?php custom_shipping_message( ); ?>