Is there a similar guide for Portal for ArcGIS 10.9.1?
Hello @Ranga_Tolapi
As per my understanding there is no similar method as well as not recommended also on higher version. However, as you are looking for 10.9.1, I would recommend looking in the "Reconfigure" option available in Portal Admin.
"The reconfigure operation re-creates the index service metadata, schema, and data in the event it becomes corrupted. This operation may take a while to finish. During this time, the index service may not respond to index queries. Keep in mind that reconfigure may not address out-of-sync indices, where the counts in the database and index do not match."
For more details refer : Reconfigure
Hope it helps!
-Archit