When the headset is disconnected, you could enter the DFU mode manually, here are the steps:

1)Close PiTool, shut down PiserviceLauncher in the task manager.

2)Unplug the power adapter

3)Plug the power adapter while the 3 buttons are pressed, the LED turns white.

4)Count 8s, release the power button, the LED turns blue

5)Another 8s, release the button in the middle, still blue light

6)1s later, release the last button, the LED should start flashing.