Unless and until Xiaomi themselves decide to implement a process to regress from Oreo, there is no realistic chance to do so.
Your only path is to restore build 2174 Oreo using the standard recovery process.
There have been internal discussions by Xiaomi developers about making public a tool to enable roll back from Oreo but, as yet, there is no decision taken.
Thanks. Any idea how I can restore to 2174? I'm not aware of the standard recovery process