1. Go to Preferences.
2. Select Cite and select the Word Processors tab.
3. Select Install Microsoft Word Add-in (or Install LibreOffice Add-in if you are using Libre).
4. Finally, make sure you tick the checkbox Use classic Add Citation dialog.
5. Next, open up MSWord and check to see that you have Zotero as one of the options on the menu-bar at the top of the page.