Here are the instructions for downgrade OnePlus 3 to Marshmallow from Android Nougat. The Nougat Beta updates were launched a few days back for OnePlus 3. The update was Beta and several users now want downgrade due to several issues yet. So we provide step by step guide to downgrade OnePlus 3 to Marshmallow from Android Nougat. This is a simple process, using that you can rollback your device to Marshmallow stable ROM. If you are one those then follow the guide completely, don’t miss any step.

Thanks to XDA member Mina Mngawy for his workaround, that will downgrade OnePlus 3 to Marshmallow from Android Nougat. The entire process is so simple but it’s completely unofficial method. You can anytime visit OnePlus Support for the official way. Anyway if you are ready and willing to downgrade OnePlus 3 to Marshmallow from Android Nougat by any reason, then go ahead and follow the entire steps.

Important: The guidelines here will downgrade OnePlus 3 to Marshmallow from Android Nougat [Unofficially] only. Don’t try on any other device. To downgrade via official way visit OnePlus Support. Also, proceed entirely at your own risk.

Downgrade OnePlus 3 to Marshmallow from Android Nougat [Unofficially].

Preparations:

• Take a full backup of the existing data on the device before downgrading process.
• Also, charge the battery of OnePlus 3 more than 80% before proceedings.
• Install USB driver of OnePlus at the PC you are using for the process. | Link
• Also, Install ADB/ Fastboot drivers on the PC. | Link
• OnePlus should already have TWRP recovery installed. | Install here

Required Downloads:

• OxygenOS 3.2.8 Full ROM Zip file. | Download Link
• Modified TWRP for OnePlus 3. | Download Link
• Stock Recovery of OnePlus 3 and Rename with “recovery.img”. | Download Link

Steps to Downgrade OnePlus 3 to Marshmallow from Android Nougat

1. Download Modified TWRP from the link above, and then flash it on the device via TWRP or Fastboot Method.
2. Then download OxygenOS from the link above and copy to the device internal storage.
3. Turn off and boot in recovery mode, allow modifications on the system.
4. At recovery go Mount and perform mount system.
5. Now go to Wipe → Advanced Wipe → Select System → Repair or Change file system → choose EXT4 file system.
6. Come back to Wipe option and → select Data → Swipe to confirm.
7. Then perform Factory Reset via →Tap Wipe → Advanced Wipe → Select all without USB OTG → then Swipe to confirm.
8. Then reboot into recovery once and Transfer the OxygenOS ROM without leaving Recovery Mode via USB cable.
9. Now tap “Install” → locate and select OxygenOS transferred file → Swipe to confirm.
10. After ROM installation, reboot the device into Bootloader Mode.
11. Now move the download Stock Recovery into ADB folder at C:\ Drive of the PC.
12. Run CMD window in ADB folder via [Press and hold → Shift+ Right click → Click “Open command windows here”.
13. Now in CMD Window issue the following command.
    • fastboot flash recovery recovery.img
14. Finally, reboot into → Recovery Mode and → perform Factory Reset
15. Done!

Source

In results, the process to Downgrade OnePlus 3 to Marshmallow from Android Nougat [Unofficially] will get successful. If you have any issue, then contact us.