this question is better to ask in the support service, many are interested in this
Went to Nokia care and got rolled back to Nougat!
How did you do that, Surendran S?
Go to the nearest Nokia Care Center and ask them for a rollback. If it is covered under warranty they'll do it at no cost. For me the version was 7.1.2, Security Patch Level: 1 Oct 2017. It'll just take only an hour time.