If the Biba button in Outlook is no longer showing in the ribbon, it probably got interrupted during install or update, and just needs to be reinstalled.
To reinstall the Outlook plugin for Biba:
From the Launchpad, select Meetings > Schedule a Meeting, which will bring up the Scheduling Assistant.
From the Scheduling Assistant, make sure Outlook is selected as your calendar, then click Schedule with Outlook.
If you don't have the plugin installed, this will kick off the installation, and you just have to follow the prompts.
When you're asked to sign in, use the same credentials you use to sign into Biba.