Android 7 To 5.1


Aug 28, 2018
Hello, I bring up this old thread instead of opening a new one.

I have a mi4c in this situation:
- LOS 14.1 (Nougat 7.1.2) recently downgroaded via TWRP from AICP (Oreo 8.1)
- TWRP (support both Lollipop and Nougat bootloader i think)
- firmware TS_libra_miui_8510
- locked bootloader

Because of some malfunctioning (cannot in any way connect to 4G, and i've no B20 problem with my actual carrier...) I would like to "reset" the phone (firmware, and other stuff) to old MIUI, and then upgrade everything up to the latest stable (think MIUI 9, i don't want to go to 10 right now)

What's the right way to do it? i've read tons of guides, but they alway start form miui roms, not stock ones like me...and they all are slightly different.
I think i have to start with a fastboot old rom and mi flash, and then unlock bootloader with mi unlock?
Could someone please help me, pointing me to the right procedure ;)