Log in to your account in the web browser or in the web app : https://web.schoolfox.com.
Select your class and click on "Settings". In the section "Teacher", you can add a colleague. For this you need his/her e-mail address. He/she then receives an invitation with a confirmation link sent by e-mail. After confirmation, the new teacher will abe added to your class.
Important: The invitation link is only valid for 24 hours. If the link has already expired on confirmation, simply reenter the e-mail address to resend the invitation e-mail.