rr os

Hello ! My Mi4C was on MIUI 8 (xiaomi.eu) with Android 6 and Android 7, updated with bootloader unlock, TWRP update and all the hard stuff. Then, I switched it to Ressurection Remis OS on Android N. All working well. I have TWRP 3.0.3-1. I want to switch again to MIUI 9, what do I have to do ...