In the Call center view mode of Virtual Call Center, click Manage Call Center Users.
Click Find to list all users or add filters to search for specific users. 
From the list of users, select the desired users and click Add to Call Center.
For agents that your account allow them to use service console, you need to enable "Service Cloud user" on the agent profile.
On Setup, Go to Administration Setup > Manager Users > Users.
Select and Edit the user and select 'User License' to Salesforce, then enable 'Service Cloud User' and Save.
