As long as you have students in a group that you own or co-teach, you can view their usernames and change their passwords from the "Members" tab in the Group.
The Username is located right below the student's name. To change a student's password, click More next to their name, then "Change Password."
Here's some more detailed info, and a screenshot:
- Go to the Group page, then click "Members."
- Locate the student in the list.
- The Username is listed below the students' name.
- To change a password, click More next to the student name, then "Change Password."