Import power, cadence and distance from mobile phone camera for "dumb" indoor cycling?

Hi!

So the indoor cycling sessions at my Gym don't have any integration with garmin or any other fitness tracking app. They do, however, have a screen that displays the current power, distance and cadence while in use, then avg power, total distance and avg cadence after 10 secs of stopping pedalling. These are the bikes: https://www.keiser.com/shop/cardio-equipment/m3-indoor-bike 

I have recently discovered I can start an indoor cycling workout on my forerunner, then manually update the avg power, total distance and cadence after the activity has been saved. However, this requires going into the activity,

I was wondering if it would be possible to create a mobile app with which the user could enter their avg power, cadence and distance after completing an indoor cycling workout (potentially using their camera and text recognition), then have this data be combined with their heartrate and time from a garmin watch.

I've never developed for garmin devices before. Is there an api for editing a user's activities after they've uploaded them? Otherwise, the communications module looks like it might be able to receive this data from a mobile app, which could be combined into FIT format.

Is this crazy? Does a solution for this problem already exist? Did I explain this really poorly? let me know!

Thanks in advance!