This article will help you with using an SSL certificate for SQL Monitor.
For SQL Monitor v. 12 and later, follow the instructions on configuring HTTPS for the default web server if you are using the built-in webserver.
If you use IIS, then we recommend that you follow Microsoft's guidance for setting up SSL on IIS: https://docs.microsoft.com/en-us/iis/manage/configuring-security/how-to-set-up-ssl-on-iis.
For SQL Monitor earlier than v. 12, you will first need to move to IIS. Please follow the documentation here for instructions on how to do this.