Go to "Monitoring" (left-hand-side menu) and then choose "SSL Monitoring". There you will find a button to create a new monitoring check.
Select "SSL Monitoring" as the type.
Enter the website name and the URL. Also, choose how many days before the expiration of the certificate you would like to be alerted.
The next step is to select when you would like to be notified if there is a problem with your SSL certificate and how often should we check it. We recommend keeping the default values.
In the end, choose who will receive the alerts.