The answer you're looking for is in the "Docs" section of the top menu.

Update your database to your website's new URLs.

Direct link:
https://www.ubbcentral.com/forums/u...transition-your-forum-from-http-to-https


current developer of UBB.threads php forum software
current release: UBB.threads 8.0.1 // wip: UBB.threads 8.1.0
isaac @ id242.com // my forum @ CelicaHobby.com