UCS Failing to sync with AD after new Windows DC was promoted and original Windows DC was demoted and shutdown

Thanks guys in advance - I really need it actually.

So I had joined the UCS to a windows AD during the install and it had been working great until a couple months back when I promoted another windows DC to take all the FSMO roles and demoted the original DC ( as it was a windows server 2008r2 and as we all know its well obsolete now).

I am using the UCS for OwnCloud for a small number of AD users and these users are still operating fine - it is just that the AD synchronization is not bringing through the new users anymore. I messed around trying to fix the issue changing DNS names etc where there were references to the old DC and changed them to the new DC but have had no joy getting the normal functionality back.

What I am looking for is a quick fix - there must be an easy way to purge the UCS’s copy of the AD info and rejoin the UCS box back to AD and get a fresh connection. keeping in ttact all the users data in OwnCloud ?

Can someone please guide me back to order from chaos…

Thank you