Adding Teachers to a workspace can be done in three steps:
Teachers should create a free Blocksmith account and request access to your workspace at: https://<yourworkspacename>.blocksmithxr.com/
The Workspace Admin must approve workspace access for those new accounts. This is the same process as approving student requests.
During the approval process you will have the option to add them as a teacher. If the teacher is already a member of the workspace you can add promote them on the teachers page on your administrative dashboard.