Hello @phalguni24, if this is a field you want to complete through a calculated field, I do believe the rank function is the best option. On this QuickSight Community topic, one of our experts provided an example function to complete the task.
I do believe that since you are utilizing Snowflake, the best case scenario would be creating the index value in your snowflake view directly or from your SQL statement when you ingest the data into your QuickSight dataset like Erik suggested.
I am going to mark this as a solution for now, but if your issue is not resolved after trying some of these options please let us know!