It seems like there is no one-click Reset feature for this tag list.
OneNote Gem - Favorites now offers a feature to reset the OneNote tag list to factory settings.
The list of tags in OneNote is customizable and displays custom tags. You can also adjust the location of these new tags
For example, the New Tag 1, New Tag 2, New Tag 3 appear in the tag list.
You can run "OneNote Gem - Favorites Fix Tools" from Windows Start Menu.
Or run "OneNote Gem - Favorites Fix Tools" from OneNote ribbon. Click "Navigation" tab -> "Options" feature.
In "OneNote Gem - Favorites Fix Tools", click "Tools" tab -> "Reset OneNote Tag List" button.
It will restore the list of tags in OneNote to the factory state.
Then, when you restart OneNote, you can see the list of tags that have been restored to the factory state.