The HT6 software only recognises the headpsets when they are connected via the included 2.4GHz wireless dongle.
Please make sure the dongle is plugged into a USB port on your computer.
Ensure the headphones are set to 2.4G mode (not wired USB or Bluetooth).
If you are using a USB cable or Bluetooth connection, the software will not detect the device – it is designed specifically to work with the 2.4G dongle.
After switching to the dongle, restart the software and try again.