Clean install is it solve, but extreme possibility. Before buy licence key for Standard edition I was finding out optionst for convert Edition and I was assured, os it is possible.
Yes, it is possible to do but not for this one in this broken state. Here one for older 2012/2016 but steps are the same for Server 2019
https://learn.microsoft.com/en-us/windows-server-essentials/migrate/transition-from-windows-server-2012-essentials-to-windows-server-2012-standard
If there were already a domain you wanted to preserve then you can easily do that.
I'd use dcdiag / repadmin tools to verify health correcting all errors found
before starting any
operations. Then stand up the new 2019, patch it fully, license it, join existing domain, add active directory domain services, promote it also making it a GC (recommended), transfer FSMO roles over (optional), transfer pdc emulator role (optional), use dcdiag / repadmin tools to again verify health, when all is good you can decommission / demote old one.
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