Reporting exercise

You should be able to go into the diary section of the app, say that you want to add exercise oh, it should be cardiovascular, and then searched in the blank box for stationary bike workouts

There's quite a few options if you search for "stationary bike" in the CV part of your exercise diary.

I would suggest going for one of the lower effort options for your calorie estimate as It's unlikely you are producing much power on one of those devices.