Before you proceed:

• Backup your important data, as the process may wipe your device.
• Make sure your device has enough battery to avoid interruptions during the process.
• Download the latest firmware for your OnePlus 3T from the official OnePlus website.

Flashing Firmware using fastboot:

1. Unlock Bootloader (if not already unlocked):

   • If you haven’t unlocked the bootloader, you may need to do so. Note that unlocking the bootloader will erase all data on your device.
   • Follow official instructions for unlocking the bootloader on the OnePlus website.

2. Download and Install ADB and Fastboot:

   • Download the Android SDK Platform Tools, which includes ADB and Fastboot, from the official Android Developers website.

3. Extract Firmware Files:

   • Extract the firmware files you downloaded from the OnePlus website.

4. Boot into Fastboot Mode:

   • Power off your device.
   • Press and hold the Volume Up button, then press and hold the Power button until the device boots into fastboot mode.

5. Connect your device to your computer:

   • Connect your OnePlus 3T to your computer using a USB cable.

6. Open a Command Prompt or Terminal:

   • Navigate to the folder where you extracted the firmware files.

7. Flash the Firmware:

   • Use the following commands to flash the firmware:

fastboot flash recovery recovery.img

fastboot flash boot boot.img

fastboot flash system system.img

fastboot flash cache cache.img

fastboot flash userdata userdata.img

Replace recovery.img, boot.img, system.img, cache.img, and userdata.img with the actual names of the firmware files you extracted.

After flashing, reboot your device using the following command:

fastboot reboot

Remember that these instructions are based on general steps for flashing OnePlus devices. The exact steps might vary slightly based on the specific firmware and version you’re using. So we can’t take responsibility for these instructions. Always refer to the official documentation and resources for your device and tools.