This feature is only available for Meeting Manager/s of the workspace.
Go to the "Members" tab in Agenda Settings. You can see all the members who are part of the workspace. Hover to the right-hand side of the member's name that you would like to remove and confirm.
This will immediately disable access for that user to this workspace. However, they will have access to other workspaces that they are part of. If you are looking to disable access to your entire Hypercontext account for a user, please refer to this article.