Had to Demote/Rename and Promote them back as Windows Server 2016 Domain Controllers. Lets see how to do it.
To list FSMO Roles –
netdom query fsmo
If they Hold It , you can move them easily using PowerShell.
Move-ADDirectoryServerOperationMasterRole -Identity DS001 -OperationMasterRole 0,1,2,3,4
Uninstall Using PowerShell –
Uninstall-ADDSDomainController -DemoteOperationMasterRole:$true -Force:$true
Or use GUI below ,
Open Server manager , Remove roles and features.
Uncheck / Remove Active Directory Domain Services.
Click on Demote this Domain Controller
Check Proceed with Removal
Enter the Administrator password
Start – Run –dssite.msc (Active Directory Sites and Services) – Delete the Stale Object Servers Object. once the replication completes
Waiting for the Replication to finish across sites rename and promote them back again. By default replication interval across sites is 180 Minutes.
Force Replication across sites – (Do Not run below on large Environments – As it lists All ADobjects and tries to sync them)
Get-ADObject -Filter * | Sync-ADObject –Destination DS0003
Force Topology Creation –
repadmin /kcc DS003
For Replication between domain controllers with existing replication links –
repadmin /syncall /AePdq