Thank you Paul,
Not sure if this was the best way, but it works perfectly. I first created a program called HVAC Fan using the admin console, with "If" remaining blank (as you suggested) the "then" to set the HVAC fan mode to circulation (an intermittent on/off mode), and the "else" to set fan back to auto. I then added the program in the portal and used "fan" as the spoken word and the Alexa category device as a switch. I then went into the Alexa app to discover the new program, now I can say Alexa turn fan on, and the HVAC fan goes into circulation. Exactly what I desired. Telling Alexa to turn it off puts it back to auto.
When I start adding my controls for the ceiling fans in the house, I'll probably amend the Alexa spoken word to house fan.
I tried to see if I can do it from just the portal, but my thermostat shows up as a thermostat under Alexa category, which then limits it to specific voice commands, as what's found in the wiki. But like I said, I've accomplished what I wanted, so thanks again.
Norm