Even if the manual is not one you created yourself, the administrator or owner can designate you as the new owner. You become the owner of a manual in the following cases:
When creating a new manual
When you create a new manual, you become the owner of that manual.
When designated as the new owner due to user deletion
When a user who owned manuals is deleted, the administrator of the folder or another user can be designated as the new owner of those manuals in bulk. If you are designated as the owner when a user is deleted, you become the owner of that manual regardless of whether you are a member of the folder or not.
Related: Delete user from group (Web Browser)
https://teachme.jp/8/manuals/8930266
When the ownership is intentionally changed
The owner of an existing manual can be intentionally changed to a third party. If you are designated as the new owner in this case, you become the owner of that manual.
Related: Transfer manual ownership (Web Browser)
https://teachme.jp/8/manuals/4929382