Please try the following steps with Word and EndNote closed.
Open Finder.
Click on the Go menu.
Click on Go to Folder.
Enter the path:
~/Library/Group Containers/UBF8T346G9.Office/User Content.localized/Startup.localized/Word
Click Go.
In the Finder window that appears delete any .Bundle files with EndNote in the name.
You should then be able to open Word and the EndNote tab should no longer appear.