Now I will do it again...
I have chinese, right?
So, I will turn on the visibility, do I need to unpair from MiFit (Google Play 4.4. version)?
I didnt unpair MB3 from official MiFit before pairing and updating it via Geek app...
Wait...
I have chinese and I want Czech...
So...turn on visibility, UNPAIR and CLOSE MiFit (I didnt do this)? Turn off and on BT and GPS and then update via Geek app...
After update via Geek app, off and on BT and GPS and open MiFit?
Unecessary unpair your Mi Band to update your Mi Fit version.
To flash custom firmware :
Activate visibility option in Mi Fit.
Unpair Mi Band from Mi Fit.
Activate GPS (and Bluetooth).
Open GagdetBridge and start Scan.
Choose your Mi Band 3 (after you do touch your Mi Band 3 to pair).
Open files explorer, choose firmware and flash it.
After Mi Band 3 restart, unpair your Mi Band 3 from GadgetBridge.
Pair your Mi Band 3 to Mi Fit.
For moment the only solution to haven't Mi Band 3 in chinese if your language isn't supported by default, it's have English phone system language to have Mi Band 3 in English.