In order to add your IT-Support team AD security group to ePO - Group Administrator permission set use the following steps:
Register your Active Directory/Domain Controller with ePO under Menu > Configuration > Registered Servers.
Then go to Menu > User Management > Permission Sets.
Select the Group Admin permission set.
Click Edit for 'Names and users' and then add the AD security group as a mapping for that permission set.
Users will need to authenticate with 'domain\username' as their username in the ePO console.
just one hint.
Activate the "Active Directory User Login" in the EPO Server Settings section to allow Active Directory User login.