This post will show you how to make the page in OneNote applcation become sub-page.
The following step will show how to make the “New Page” become a sub page under “Overview” tab.

Step
- Original of the document will shown as image.

- Select the “Overview” tab and click on the down arrow button beside the “New Page”. After that click on “New Subpage”.

- System will created a new sub-page called “Untitled page”.

- Then, select the “New Page” Tab. Hold and move the page above the “Untitled page” and release it. Now it should look like as image.

- Then delete the “Untitled Page” and now your mission was completed.
Hope you’re benefit from it.