1. Go to the admin panel by adding wp-admin to the site domain string (for example, site.com/wp-admin).
2. Go to the main WordPress menu by clicking the Wordpress logo. In the menu go to the Appearance - Editor section.
3. In the theme editor open header.php (header).
4. In the header.php (header) edit box, paste the button code (see the detailed instruction in the article) and click Update file.