Install official CM14.1 Android 7.1 Nougat ROM on OnePlus 3. CM14.1 Android 7.1 is an experimental build but stable ROM for One Plus 3.
the guide mentioned below is only for OnePlus 3 and cannot be tried on any other device or variant. You can check device model by going to Settings >> About Phone.
Update OnePlus 3 to Android 7.1 Nougat via CyanogenMod CM14.1 Custom ROM
Take a complete backup of data,apps and settings as the procedure may wipe your data.
Make sure that the battery of device has a minimum charge of 60%.
Enable “USB debugging” on your device.
Install the ADB and fastboot drivers on your PC.
Connect your device with computer via USB cable.
Copy/paste the downloaded Android 7.1 ROM zip and Google Apps zip files to your SDcard root folder.
Switch off your device.
Enter Recovery. Hold power button and volume down button and enter recovery.
Select “wipe data/factory reset”, wipe cache partition” and in Advanced select “Wipe Dalvik Cache”.
Select “install zip from sdcard” and then select “choose zip from sdcard”. Navigate to “Android 7.1 ROM” file which you have downloaded and confirm to “install”. Wait till it gets installed.
Repeat the procedure to install Google apps by selecting “choose zip from sdcard” and then select “Gapps.zip” and install.