How to fetch tracked data from *mi Fit* Android app?
If it is acceptable for you to use a separate app to collect this data, take a look at GadgetBridge (available on F-Droid). That's an open source app supporting many gadgets, a.o. Pebbles and Mi-Bands. It allows you to export the collected data (see e.g. here). Since v0.24 you can even set it up to do so automatically/periodically.