When you create a new page in OneNote, the first line of text you type becomes the name of the page. If the page is blank, the page is just called “untitled page.”
You can rename a page anytime.
Right-click the page tab, and click Rename.
Type your new title over the highlighted page title at the top of the page.
You can also click the page title area on the top of your notes page to change the name. But if the page title is hidden, you won’t be able to select it. If you don’t see a page title area on the top of your notes, click View > Hide Page Title. This button hides and shows the title area. After it’s visible, you can rename the page.