To reset your Sony H900N headphones, please follow these steps:
1. Make sure the headphones are turned off.
2. Plug one end of the USB cable into the headphones and the other end into a USB power source.
3. Press and hold the power button for at least five seconds.
4. The headphones will turn off and then on again, indicating that the reset is complete.
If you are still having difficulties resetting your headphones, please contact Sony Support for further assistance.