This documentation will show you how to add Site Title and Tagline to your website.
When you are on SiteBuilder dashboard. Hover on Settings tab in left menu and then click on General.
Once on General Settings page you will see editable options like Site Title, Tagline, Date Format, TimeZone, Time Format, Week Start On etc.
Enter the Site Title and Tagline for your website once you add it. Click on Save Changes button.