https://www.androidsage.com/2017/03/28/install-oxygen-os-4-1-1-for-oneplus-3-and-3t-with-upgraded-android-7-1-1-nougat-download-ota-and-full-rom/
Install Oxygen OS 4.1.1 for OnePlus 3 and 3T with upgraded Android 7.1.1 Nougat [Download OTA and Full ROM]