If your Oppo is completely dead due to battery planting, then you need to charge the battery first before trying to turn it back on.
The method is as follows:

1. Make sure you have a charger that matches your Oppo, then plug the charger into the socket.
2. Connect the charger to the USB port on your Oppo, then wait for the battery to charge.
3. Once the battery is sufficiently charged, press and hold the power button for a few seconds until your Oppo turns on.
4. Once your Oppo turns on, release the power button and wait for the system to finish restarting.
5. Once your Oppo has finished restarting, you can use it as usual.

Make sure to always charge the battery regularly so that your Oppo is always ready to use.
Also, avoid using your Oppo until the battery is completely discharged as this can cause the battery to erode or even damage.
If you are experiencing problems with your Oppo battery, we recommend contacting Oppo’s support service for further assistance.