I have a Splunk cloud and trying to find where to configure S3 Bucket info for smart store?
You don't. Splunk does that for you.
Can I get access to the S3 storage account for my instance or can i provide my own S3 storage account?
As per above article, user can configure their own S3 account for smart store?
DDSS lets a user define an S3 bucket for storing expired buckets. It is not used for SmartStore. DDSS is enabled for each index (Settings->Indexes then click an index name, select the DDSS button, then click "Edit self storage locations"). See https://docs.splunk.com/Documentation/SplunkCloud/8.1.2103/Admin/DataSelfStorage?ref=hk#Configure_se... and https://lantern.splunk.com/hc/en-us/articles/360043201234-Archiving-data-in-Splunk-Cloud