DAY2 Cost Summary insights are enabled by AWS Cost Explorer service. Please follow the below steps to setup AWS Cost Explorer.
Setting up Cost Explorer
Sign in to the AWS Management Console and open the Billing and Cost Management console at https://console.aws.amazon.com/billing/home#/costexplorer
On the navigation pane, choose Cost Explorer.
On the Welcome to Cost Explorer page, choose Launch Cost Explorer.
4. For EC2 instances granular cost insights. On the navigation pane, Choose Preferences, then select the Hourly and Resource Level Data and click on Save preferences
For permissions & cost associated with AWS cost explorer refer Analyzing your costs with Cost Explorer - AWS Billing and Cost Management (amazon.com)