But, if you have a large number of notebooks, it is difficult to drag and drop.
Gem for OneNote v28 now provide features to move top or move bottom a notebook.
Select a Notebook
At first, choose a notebook we want to move to top in OneNote.
Next, Click "Gem for OneNote" feature "Gem" tab -> "Sort" group -> "Notebooks" menu -> "Move Notebook to Top" menu item.
This feature move current Notebook to top of OneNote notebook tree.