1) Download OxygenOS 4.1.0 zip file from above and save it inside the folder where ADB files are installed.
2) Reboot your phone into Recovery Mode by turn off the phone and holding the Power and Volume down buttons.
3) Now in recovery, choose “Install from ADB” and tap OK to confirm.
4) You see a screen with “You are in sideload mode”.
5) Connect your device to PC/Mac and run the following command.
adb sideload file name.zipFor Mac/Linux:
./adb sideload file name.zip
6) Now wait for a while for the device to update.
7) Done! Your device will automatically reboot to OxygenOS 4.1.0.
Follow the above guide to Install OxygenOS 4.1.0 on OnePlus 3/3T or alternately you can flash the full ROM via TWRP Recovery. If you have any question related to this post, feel free to leave that in the comment section.