If you have difficulty with the below or still encounter issues after doing the below, please have your hosting provider remove the HTTP to HTTPS redirect on the server as it may be battling the software.
The conf_global.php file is located in the root of your installation directory. Based on your URL, this should be in a directory called "discussion". You will want to contact your hosting provider for a full path to the directory.
Once you change the URL in your conf_global.php file, you will want to clear your cache by going to ACP -> Support -> Clear System Cache. That will update all URLs in the software itself. You will need to update any manual URLs.
Unfortunately, as you are self-hosted, this is self-managed so we can help guide you with software questions but anything hosting related, you will want to contact your hosting provider or server administrator for assistance as that would be outside our scope of support.
If you do not wish to handle any of this and rather just manage your community, have you considered our Cloud?: https://invisioncommunity.com/buy