Pacer in custom workout

I want to create a custom running plan in the workout app on my Apple Watch to run 1 km at a certain pace, run for 90 seconds at a different pace and repeat it multiple times . I tried to create a custom workout in the app but pacer mode don't seem to show up (only open, distance and time workouts pop up when I click add), as I want the watch to keep myself in track in my wanted speed. Is there a way to fix this issue? or something alternative?