• Download the Plugin
  • unzip it and upload wp-ban-registration-domain to wp-content/plugins
  • Login to Dashboard
  • Visit Dashboard->Plugins->Installed or Dashboard->NetworkAdmin->Plugins->Installed(If you are using multisite) and activate the “WordPress Ban registration Domain”
  • Please Visit Dasboard->Settings->Ban registration domain and include the domains/emails/extensions you want to block
  • that's it.

Alternatively, you can use the WordPress plugin installer to upload and Install the plugin.