When you first insert a citation, a bibliography is created at the end of your Pages document.
To delete a bibliography, select the entire bibliography, and then delete it.
Make sure you drag the cursor from the line above the bibliography to the end of the bibliography in order to select the entire bibliography field. Press the Backspace or Delete key.
Pages will assume that you do not want a bibliography at all, unless you specifically insert one again.
To insert a bibliography:
Place the cursor where you want the bibliography to start.
From the Insert menu, select EndNote Bibliography.
Note: If you have not first deleted an existing bibliography, it will become plain text. The text in the old location will never get updated, and the bibliography in the new location will change as you add or update citations.