Customizing a CloudFormation template
First, copy the URL from the box on Boomerang. Then Go to the CloudFormation service on the AWS web console(https://console.aws.amazon.com/cloudformation/).
Click 'Design template', it will direct you to AWS CloudFormation Designer console.
Click the file icon on the top left corner. Click 'Open' and choose the 'Amazon S3 Bucket' icon. Paste the template URL and click 'Open'.
After the console finishes loading, you will see the graphical resources infrastructure described by the template.
You can customize the template either by graphical view or text view.
See more details about how to modify template in AWS CloudFormation Designer:
After you modify the template, you can click 'Create stack' button to create a new stack.