Hi there :)
That documentation page is useful at https://www.virtualmin.com/documentation/web/ssl#installing_a_certificate
But we suggest to update it. In the latest Virtualmin version 4.18 we noticed that the wording changed.
The following line: "Go to the Manage SSL Certificate page, and click on the New Certificate tab."
Should read: "Go to the Manage SSL Certificate page, and click on the Apply Signed Certificate tab."