How to make phone number become whatsapp link in back-end order details woocommerce

add_action( 'admin_footer', function() {
    if ( get_current_screen()->post_type == 'shop_order' ) {
?>
<script>

    jQuery( function($) {

        function tel_to_wa() {
            var wa="//wa.me/51";
            var tel = $( 'a[href*="tel:"]');
            tel.attr({
                href: wa + tel.text(),
                target: '_blank'
            });
        }

        tel_to_wa();

        $( '.order-preview' ).click( function() {
            $(document).ajaxComplete( tel_to_wa );
        });

    });

</script>
<?php
    }
});