Hi There,
Thanks for writing in! Because this requires a template change, I’d advise that you setup a child theme. This allows you to make code changes that won’t be overwritten when an X update is released. After your child theme is setup, please review how we recommend making template changes in Customization Best Practices.
Then add this on your child theme’s functions.php file.
add_action('wp_head','my_verification');
function my_verification () { ?>
<!-- verification code here -->
<?php }
Replace the <!-- verification code here -->
with your actual code.
Hope it helps, Cheers!