1st Step: Create a duo teacher.
In My Studio > Teachers > Add a teacher.
Mention their email address
Write the first teacher's name under 'First Name' and the second teacher's name under 'Last Name' > Save
2nd Step: Assign the duo teacher account to your activity.
In Calendar > Add sessions > Choose the activity > Confirm.
Fill in the form > Search for the duo teacher account created before > Substitute.
> Create the sessions.
Now the sessions you have just created are associated with a teacher duo.