Add WooCommerce customer username to edit/view order admin page

functions.php

// Add WooCommerce customer username to edit/view order admin page 
add_action( 'woocommerce_admin_order_data_after_billing_address', 'woo_display_order_username', 10, 1 ); 
function woo_display_order_username( $order ){ 
global $post; 

$customer_user = get_post_meta( $post->ID, '_customer_user', true ); 
echo '<p><strong style="display: block;">'.__('Customer Username').':</strong> <a href="user-edit.php?user_id=' . $customer_user . '">' . get_user_meta( $customer_user, 'nickname', true ) . '</a></p>'; 
}