Confirmation emails can be re-sent from the SNS console. To find the name of the SNS topic associated with the alarm, click the alarm name within the Route 53 console and looking in the box labeled "Send notification to."
Within the SNS console, expand the list of topics, and select the topic from your alarm. Open the "Create Subscription" box and select Email for protocol and enter the desired email address. Clicking "Subscribe" will re-send the confirmation email.