1) Install both WooCommerce and the plugin.
2) Set a WooCommerce shipping method, and the store's address to one that is in Vietnam.
3) Add product to cart, and proceed to checkout
4) Tick "Ship to a different address?"
5) Fill the telephone field with:

" onmouseover="alert(1);//

An alert box should pop up when an administrator hovers the order's associated recipient phone number on http://vulnerable-site.tld/wp-admin/post.php?post=$ORDER_ID&action=edit

You can find a video here: