How to remove "HTTPS" from Admin URL during site signup?

I have SSL installed on the main domain -> https://MainSite.com but NOT on the wildcard http://SubSite.MainSite.com. After the subsite creation, user is given the brief welcome messages contain login details: subdomain URL and login URL.

The login URL is supposed to be HTTP://SubSite.MainSite.com/wp-login.php but is automatically set to HTTPS://Subsite.MainSite.com by your code.

Please advice without granting access which part of your plugin I need to change apart from uninstall the SSL from the main site.