Here's how to insert and format individual citations for different works by the same author(s).
First, use Cite While You Write to insert your desired citations at the appropriate location within the text.
Highlight the citation within the text. Select the "Edit & Manage Citation(s)" option in the "EndNote X8" tab of the menu ribbon in Microsoft Word.
Within the Edit & Manage Citations window:
You are done! As always, check your citations for accuracy.