In the User Attributes section, administrator need to specify the AD group in LDAP syntax. For example, Domain Admins groups is as below:
CN=Domain Admins,CN=Users,DC=example,DC=com
If Directory Sync is enabled, you can also naviagete to the Group section. locate the LDAP group and open details.
In the LDAP Group section, click the Copy LDAP Group to Clipboard option and then paste it back to the User Attributes Section