You can navigate here to add users to group.
https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/plan/security-best-practices/appendix-e--securing-enterprise-admins-groups-in-active-directory#step-by-step-instructions-for-removing-all-members-from-the-enterprise-admins-group
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If under the situation all root / parent domain controller was corrupted. How can we give child domain controller administrator account have enterprise admin and schema admin to seize the naming master and schema to child domain controller?
Understand Enterprise Admin and Schema Admin only available in Root / Parent Domain Controller.