When being added to a workspace, all users are given the participant role automatically.
Besides the admin who has created the workspace, you might want to give some other users admin rights as well.
How to add admin role to a participant:
Access Workspace Manager
Open the Admin Menu.
Click on Workspace Manager.
Navigate to the Users tab
Open the "Users" view in the Workspace Manager.
Find the participant you want to give admin rights to
Open the "..." menu on the right side
Click "Add admin role"
A workspace admin can also remove the admin role from another user the same way: