The starter should have an Office365 account, because SCC is working with O365 login.
Someone who has admin permissions on the SCC backend will go to the SCC Support queue and invites the new person to the queue. For this please follow the next steps:
Go to: https://contactcenter.stellarise.com/index.php/contact-centers
After logging in you will see the contact centers, please open the Stellarise Contact Center: 
Then go to Manage Queues: 
Click on the Support Queue: 
Then write in the email address and click Invite Agent: 
That's all, after this he will receive an email, and he needs to follow the instructions there.
Clicking on the link inside the email he can setup his password and then will get a User Guide: how to setup the SCC extension and he is good to go.
Basically he will need to download the extension from the user guide, install it in Chrome or Edge and then logging in with his Microsoft account, then setting up his phone number in the settings and he need to make sure the 'do not disturb' is off and notifications for the browser are allowed on his machine.
Once these steps are done properly he will have a fully working SCC extension where he can answer the calls from clients.
If you having issues please contact with Ors on Teams.