The online knowledgebase instructions were incomplete and overly complicated. The best existing instructions I could find are here:

The better process which I followed based on a support call are as follows:

Procedure:

1)      Copy the wildcard certificate PKCS12 (.pfx) file to: 
C:\Program Files\ManageEngine\AssetExplorer\conf\ folder

2)      In the same folder, open the server.xml file in a plain text editor.

a.       Search by the keyword "keystorepass" and replace the values for the following fields:
keystoreFile="conf/name_of_cert_file.pfx"
keystorePass="xxx-big-long-string-of-characters---your cert-password-string-xxx"
keystoreType="pkcs12"

3)      Update the Web server port and protocol:

a.       Open an administrative CMD prompt

b.       Navigate to the bin folder:  C:\Program Files\ManageEngine\AssetExplorer\bin

c.       Run the bat file with the port and protocol switches – like this: 
changeWebServerPort.bat 443 https