If you need to give more granular permissions for accessing books in a personal account, you can convert the personal account to an organization.
Warning: Before converting a user into an organization, keep these points in mind:
You will no longer be able to sign into the converted user account.
An organization cannot be converted back to a user.
You cannot access books that belong to an organization unless you are one of its members. As a result, you'll need to create a new user account that will let you access the organization later.
If the user you're converting is already a member of other organizations, you must first leave the other organizations.
Open your account settings.
Under "Transform account", enter the username of your new personnal account (see section 1.), click
Turn into an organization.
If you added your secondary personal account as the new owner in the last step of the conversion process, sign in to that account, and in the account context switcher, you'll be able to access your new organization!