[Honor 5C Guides, News, & Discussion] shashank1320:
Detailed guide to downgrade from Nougat (unofficial or beta) to Official Marshmallow.

Saw many users struggling with unofficial Nougat update (via firmware finder) and were looking for downgrade procedure (on Facebook, honor community and on XDA) to go back to stable and official Marshmallow version from Beta/stable stock Nougat version. Below method is thoroughly checked personally by me for more than 5-6 times and I am writing this detailed step by step guide for downgrade.

Prerequisites-

Non-rooted phone (no changes to the system partition and bootloader made)

Make sure you are running the Nougat version B3XX (not custom ROM)

Make sure you are on stock recovery.

Make sure to take full backup of the data and apps as this downgrade process will erase all your data and will wipe the internal memory. (you can use this backup to restore your contacts, call/sms logs, app with data, your home screen layout etc.)

Make sure your device is charged to at least 50%.

SD card with minimum 4 GB free space (as main product package is around 2.77 GB in size)

Let’s start the process.

Updating product transfer package-

Download the update.app product transfer package for Honor 5C device from link https://goo.gl/KYZ3Pd

Create a folder dload in the root directory of your SD card.

Copy the update.app package which you just downloaded to dload folder.

Power off the phone.

Press volume up+volume down keys and simultaneously press power button.

Your phone will automatically detect the package and will start the update process.

Once the update process is successful, you will get a message as update was successful and your phone will restart automatically

.

Updating the main product package (Marshmallow B151 package)

Delete the old dload folder from SD card. (which had transfer package file of size 69 MB) - Do not forget to delete this folder or rename it or else the same file will be keep on flashing again and again.

Download the full version package from the link https://goo.gl/8d4s73

Copy the entire folder with UPDTAE.APP file in it to root directory of SD card.

Power off the phone.

Press volume up+volume down keys and simultaneously press power button.

Your phone will automatically detect the package and will start the update process.

Once the update process is successful, you will get a message as update was successful and your phone will restart automatically.

During restart, phone will verify the system image.

This verification and 1st boot may take upto 4-5 minutes so do not panic.

Once the phone is booted and up, it will ask for the initial setup like language, wifi, agreement etc.

Validation-

Once the phone is setup, go to setting—about phone—check the android version and build number to verify you are running on Android Marshmallow version.

NOTE:

This process will completely erase your data, so make sure to have a backup before proceeding further.

This process will downgrade your phone to Android marshmallow, EMUI 4.1.2 and B151.

I have personally tested this method and downgraded my phone to marshmallow without any issue (10+ times)

If you follow the guide correctly, you should not face any issue with condition that all the Prerequisites are met and you followed the steps in order.

If anyone still have any doubt or a slight hesitation, please feel free to ask in the comment before proceeding and risking your phone.