Outdoor cycle has disappeared from my watch

In the workout app scroll down to the bottom and tap on "add workout",a large list of workout types will appear.

Just tap on the one that is missing and it will be added back to your list of workouts.

I would look at the apps you have enabled on your watch. If it doesn't show up there you should try reseting your Apple Watch to factory settings and restore it from a backup. If it does show up, re-enable the app.