Skype for Business 2016 for Mac
In the Finder menu, click Go, then Go to Folder.
Type ~/Library and press Go
Delete the following files:
- .../Library/Saved Application State/com.microsoft.SkypeForBusiness.savedState
- .../Library/Internet Plug-Ins/MeetingJoinPlugin.plugin
In the Finder menu, click Go, then Utilities.
Open Keychain Access.
Delete Skype for Business Keychain, then Empty Trash.