I want to use Splunk app for aws to monitor my aws instances. For that reason, I want to add my aws account to Splunk app for aws, but when I go to configure section of "Splunk app for aws" I don't see a place/section to add aws account information.
You need to add the Splunk Add-on for AWS to setup your credentials and inputs. You can either use your Access Key / Secret Key for the credentials, or you can grant your AMI access via an EC2 role. The second option is if you are running the AMI in your AWS deployment.
The Add-on can be found here: https://splunkbase.splunk.com/app/1876/