Hi @nige, please firstly press all physical buttons at the same time (do not connect the headset), and then just plug the USB cable of the headset to a port 2.0 / 3.0, and then loose power button after 8 seconds, meanwhile keep other 2 buttons in 8s, then loose middle button and keep pressing the last button in 8s,
then you should see the light is flickering, it means the headset enters to DFU (Firmware update) mode. If not, please operate above again.
When the light is blinkering, please send ID & Password of Teamviewer13 to firstname.lastname@example.org, I would like to assist you remotely. Please be advised.