Boot to your TWRP recovery and backup the NVRAM and NVDATA partitions (Tap on backup and optionally uncheck any partition except NVRAM and NVDATA and swipe to the right to backup). Now tap on wipe and slide to the right to wipe.
Go back to main screen and tap on « Advanced Wipe » and check « Dalvik/Art Cache« , « Cache« , « System » and « Data » and then slide again to wipe. <= This step is crucial!
Go back again and tap on Install, choose CyanogenOS-13.0.2_C8.zip (tap on Select Storage to choose the storage on which you stored the zip file) and swipe again to the right to install.
After the restore process, flash the Fix-C8_Marshmallow.zip file the same way as in the previous step. This step is optional if your previous rom was a Marshmallow ROM.
Optionally flash the Google Apps package. If you don’t flash it, you won’t have Google Services like Play Store, Gmail, Hangouts etc.
Tap on reboot once finished. First reboot can take a long time.
If you don’t have network or SIM card isn’t detected, boot to TWRP and restore the NVRAM and NVDATA backup you did on the first step.
Credits and Thanks
Syed Ahmed Ali Shah
Anyone else I may have forgotten to mention
Disclaimer :- If You May Get Bricked During Flashing Process So We Or I Am Not Responsible.
Guitar is my second most favourite language ... what ? lol yes.. i love guitar and singing.