Hello Sibs3000,
It sounds like you have a question about setting pace for your run in the Workout app on your Apple Watch, right?
Have you tried starting a new workout and see if you're able to set that limit? What about restarting your watch? Check out this article that may help:
Run with your Apple Watch
"How to start a running workout
- Open the Workout app.
- Scroll to Outdoor Run or Indoor Run.
- Tap the More button
to set a calorie, distance, or time goal. To set a goal-based workout, or to complete a Pacer or Custom workout, tap the Edit icon
next to your goal. - Tap Start.
- Wait for the three-second countdown. To skip the countdown, tap the screen.
To check your progress, check your watch face. Pace alerts are available for Outdoor Run only.
If you have Apple Watch Ultra, you can set your running workout to the Action button."
Regards.