How do I use Shortcuts to change Watch Face?

I saw a video recently where someone talks about their watch faces, such as work out, or during the day.

doing it on the watch is one of those wake... press firm and hold... swipe... swipe... swipe..............

I assume this can be done in Shortcuts on the iPhone. So you go into it, tape "Activity Face" for example, and it's done. Or better yet: Siri Shortcut Activity face....

How do you do this?

I did look at setting one up, but after Set Watch Face, I see no options that list my Watch Faces.

Hope someone can help.

Simon