Add or remove co-teachers in Class Notebook for OneNote

Co-teachers have the same access as the teacher who created the Class Notebook to open and manage class notebooks from any device.

Sign in to Office.com with the log-in provided by your school.
Select Class Notebook, then Add or remove teachers in the Class Notebook Wizard.
Add teacher(s) by name or email address. Remove teacher(s) by selecting their name.
Confirm the list of teachers with access to your class notebook.
Select Update.

The teacher(s) you added will receive an email with a link to their notebook.

Source: Microsoft