Apart from the above solution you can create the contact type "key User" from the
"Service Control Center" work center.
1. Go to Contact Details
2. Select the button Add Contact.
in this new window , you can select the user who already have "Application and User Management"
work center assigned as a contact type Key User.
This will create a new request that will be approved by SAP and user will be update as Key User in
SAP Contact.