You can configure this by going to Manage My Subscription > Manage Subscription and scrolling down to the Users section. If you choose to Hide Tab from Unlicensed Users, anyone who isn't included in the Subscription list will not see the Help tab. You have the option of uploading a list of users you would like to assign a license to, and who will therefore see the Help tab. If you would like to hide the Help tab from one or more users, but not from all unlicensed users, you should configure your subscription to Hide Tab from Unlicensed Users, but not Block New Users:
Once your subscription is configured this way you can go to Manage My Subscription > Users > Blocked Users and click on +Add User to add users individually. You can also create a CSV file of FirstName, LastName, Email and clicking Import Blocked Users to upload your blocked users in bulk.
Once configured this way, anyone who is in the Blocked Users list will not see the Help tab.