Nothing called as folio number on my physical share certificate

My father is holding a physical share certificate from SBI dated November 1991. I can only see Certificate number (four digits) but there’s nothing called folio number. This certificated is with FV RS.10 and I need the folio number to get certificate with FV RS.1. Please suggest me what should I do. I want to de-materialize it.

Process for converting physical share certificates into Demat form mentioned here .