Auto Scaling group - Scaling DOWN
Firstly, you need create an alarm.
Whenever the Minimum of CPU Utilization is less than or equal to 30% for at least 1 consecutive period of 5 minutes, Scale DOWN.
Set all fields as shown below and click on Create Alarm.
After that, you have to set the action on the policy.
When the alarm goes off, remove 1 instance and then wait 300 seconds before allowing another scaling activity.
Set all fields as shown below and click on Save.
After created, the policy will be listed on Policies section.