How do I use the Alternate Hreflang module for on-page Drupal SEO?

https://www.drupal.org/project/hreflang

About Alternate Hreflang module

The Alternate hreflang module automatically adds hreflang tags to your pages. Search engines reference the alternate hreflang tag to serve the correct language or regional URL in search results which is important for multilingual websites. In Drupal 8, the Core Content Translation module does already add hreflang tags to translated entity pages. Hreflang tags should be added to all pages, even untranslated ones. This module takes care of this for you.

Install and Enable the Alternate hreflang module

  1. Install the Alternate hreflang module on your server.
  2. Go to the Extend page: Click Manage > Extend (Coffee: “extend”)
  3. Select the checkbox next to “Alternate hreflang” and click the Install button at the bottom of the page. There are no permissions to set or further settings to change.