How to get VO2 MAX assessment without 'run or bike ride'?

The watch is calculating a VO2max if you wear the watch during the day or during outdoor run, bike with power meter or trail run.

If you want an accurate VO2max, go the a test laboratory. 

thx. I just don't understand why this watch generated VO2 MAX score even when I never recorded outdoor run or ride with power meter :(

As I said, it will generate a VO2max even because you're wearing it during the day.

ah, it's a different explanation from Garmin offers. not only by run or ride. thank you!

It is exactly what Garmin says: support.garmin.com/.../

get it . thank you very much 

As it is possible to manually edit your workouts, if I manually enter my average power and max power into the indoor cycling workout summary, would this be sufficient alongside the HR data to generate a VO2 max? 

3027952 said:

if I manually enter my average power and max power into the indoor cycling workout summary, would this be sufficient alongside the HR data to generate a VO2 max?

No. the watch needs to get the real time info.

What do I need to do buy to do this? Thanks 

It will also give you VO2max during an outside walk.