Go to Settings > Integrations and Keys, click New key, and search for CloudWatch. Select the item and click Continue.
In the Configure AWS Cloudwatch dialog, specify a key name and your AWS region, and click Save.
In the Integrations list, where your key is now included, click Authenticate.
Enter the access key ID and secret access key and click Save.
Now that you've configured your integration, add one or more of the integration's actions to an automation, test the automation, and then add the automation to an incident type.