Hi@akhtar,
You can attach one or more EC2 instances to the specified Auto Scaling group. When you attach instances, Amazon EC2 Auto Scaling increases the desired capacity of the group by the number of instances being attached. The below example attaches the specified instance to the specified Auto Scaling group.
$ aws autoscaling attach-instances --instance-ids i-93633f9b --auto-scaling-group-name my-auto-scaling-group