Hello,

Please contact your host support perhaps they make automatic backups of the site. Try to restore your site.

Each time you want to test something, install a new plugin, or update the theme aways make the full-backup of the site. Changing the demo reset all the theme settings.

Now you need to find your home page and set in the General > Reading, then find the header builder and set is as default if you cannot restore the site.

Best Regards