Go here and read
https://xiaomi.eu/community/threads/7-2-9.38201/
and do this..
How to upgrade to Andoid 7.0:
Install MIUI 6.12.22 before updating to Android 7.0..
Select zip in Updater - menu - select zip
Unlock your bootloader again on Mi4C, Mi4S, MiNotePRO
(check your bootloader status by...