It appears that the Calendar app saves its login info somewhere and doesn't give a way to update it once it's entered. Even if you unsubscribe from a calendar and resubscribe, it pulls the original log info from somewhere. That's what I'm seeing when I tried it on Catalina. I looked in ~/Library/Calendars and deleted the cache files but that didn't help. I also looked through all the .calendar folders, but none of the older items were for the BandHelper subscription. Finally I deleted that whole folder to complete reset the Calendar app, but it still was pulling my old login info from somewhere.
You could contact Apple to see if they have a solution. Or you could unsubscribe from the secure URL and use the Open URL on the Settings > Schedule Sharing page instead.