Create Automation rule

Bhavini 

You would need to resort to using a logic app with an incident trigger.

The alert counter is already included in the incident info, so all you need to do is create a condition based on this very value:

Bhavini I don't think that condition is available in the automation rule, you can only change the severity of an incident when an alert is added but the specify the number of alerts, as far as I know that option not available yet.