I have an ancient OnePlus 6 which my son uses for watching cartoon. Recently its power button stopped working and my son drained its battery until it shutdown. Fortunately its volume buttons are still working.

For this you will need a laptop and a USB-C cable to connect the phone with the laptop.

1. Ensure the phone is charged.
2. Remove the cable from the phone.
3. Press the volume down button. Keep it pressed.
4. While keeping the button pressed insert one of the of the cable into the phone and the other end in the charger or laptop or power bank.
5. Still keep the volume button pressed until you see something on the screen. Then release the button.
6. You will now get into phone’s recovery menu. Some versions of One Plus and other Android phones have restart option right here. If yes then choose that and you are done. – Else continue below –
7. In my case; in OnePlus 6; I had to choose Advanced option and within that it had “Reboot to fastboot” and “Reboot to recovery mode”. Choose “Reboot to fastboot” here. But wait!
8. First goto your laptop and install ADB tools from Google. Choose one from the following based on your laptop’s operating system.
   • Windows – Download File: Download
   • macOS – Download File: Download
   • Linux – Download File: Download
9. Extract the contents of the above zip file. Now choose the “Reboot to fastboot” option on your phone. Without this you will not able to turn on or off your phone until it runs out of battery since this mode requires the use of power button to confirm the selection.
10. Connect the phone to the laptop using the cable then go into the extracted zip file’s directory and run ./fastboot devices to confirm that your phone is detected.
11. Finally run ./fastboot reboot this will respond with a “Ok” response and your phone will reboot into normal mode. Congrats!