After creating a new v3 key, where do I update the key on my website?

This depends on your website's setup. If you're using a CMS (like WordPress, Drupal, or Joomla), you'll likely update the key in the reCAPTCHA plugin settings. If you're using custom code, you'll need to update the 'site key' in the HTML where reCAPTCHA is implemented and the 'secret key' on the server-side where you verify the reCAPTCHA response.