Once your lab machines are started you should be able to click on the Open Console button which opens a window. To login to workstation machine use student user and student as the password.
You should be able to see these details in the Orientation to the Classroom section of each course.
If you are still facing issues please raise a support ticket at access.redhat.com (choose Product - "Red Hat Online Learning") and the team will assist you.
Happy learning and stay safe!