CAUTION: This solution involves deleting Skype for Business files and folders. If you accidentally delete incorrect information, you may have to uninstall and reinstall Skype for Business.

1) Close all open applications on your Mac, including Skype for Business.

2) In your Mac's menu bar, click Go and choose Go to Folder.

3) Type /Users/your_username/library and click Go.

4) Find and delete the following folders and files:

CAUTION: Only the delete the files or folders in bold.

• /users/your_username/library/Containers/com.microsoft.SkypeForBusinesss
• /users/your_username/library/Internet Plug-ins/MeetingJoinPlugin.plugin
• /users/your_username/library/logs/LwaTracing
• /users/your_username/library/Saved Application State/com.microsoft.SkypeForBusiness.savedState
• /users/your_username/library/Preferences/com.microsoft.skypeforbusiness.plugin.plist
  

5) In the top right-hand corner, click on the Spotlight search icon. Type Keychain Access and press the return key.

6) Delete all Keychains that begin with "Skype for Business."

7) Restart your computer.

8) Sign in to your computer and open Skype for Business. A new profile folder will be built automatically in the locations above.

Outcome

You have a new Skype for Business profile.