Unfortunately, it is not possible to join a class from a teacher account.
However, you can still join another teacher’s classroom by creating a student account. You can even use the same email address that you use for your teacher account!
If you do join a class as a student, keep in mind that you won’t be able to share the assignments from the class with your own students. Click this link to learn how to join as a student: https://support.edpuzzle.com/hc/en-us/articles/360007544272-I-m-a-teacher-can-I-create-a-student-account-