How to set 24 hour time format on my Apple Watch

I think he’s got a typo. It the Watch app on your iPhone, not Settings app on your Watch.

How to set your watch to 24-hour time

1. Open the Apple Watch app on your iPhone. 
2. Tap Clock. 
3. Turn on 24-Hour Time.

His link shows the correct information on setting 24 hour time, as I outlined.

Let’s get this issue of yours resolved though. If you turn on the 24 hour time in settings, the time on all your digital display Watch faces will be 24 hours. If that setting is not turned on, your only watch face with 24 hours time is as Jeff Donald stated the World Time Watch Face and Solar Dial, which can both support 4 complications.

Turn on 24 hour time on your Watch ⇢ Change the time settings on your Apple Watch - Apple Support

To set your time to 24 hour time on your Apple Watch, go to Settings > Clock > then scroll down to 24 hour time.

Change the time settings on your Apple Watch - Apple Support

If you cannot do it on your Watch for some reason, try it in the Watch app on your iPhone. Open the Apple Watch app on your iPhone, open Clock then 24 hour time.

In addition to Zachyy’s excellent comment, the World Time Watch Face in the Face Gallery supports 24 hour time.

Any of the digital display support 24 hour/military and the World Face and Solar Face both support it, I believe.