How to set up cardio interval workouts on my Apple Watch?

I'm trying to set up a cardio (any activity) interval workout - 3 minutes intense, 3 minutes slower for recovery. Every time I try following one of the instructions, I wind up with a once only setup.

Are there any preset ones out there I can download to my watch? or tips to set them up as a separate new workout category?

thanks,

tom

[Re-Titled by Moderator]

Original Title: Help with custom cardio interval workouts