official Firmware installation With Stock Recovery-
1. Download the software build for your device From here.
2. Plug your phone into your computer and copy the downloaded .zip to your phone’s storage. If you’re using a Mac, you can install Android File Transfer for this operation.
3. After the .zip file is copied to your phone, reboot your phone into recovery mode. To do this, shut down your device and turn it back on while holding the power and volume down [oneplus user] [volume up other user] buttons simultaneously.
4. Choose “Install from internal storage/Install from local”, find your .zip file and click on “Install” to confirm.
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