Could you please start Device Manager and check if there is a Guillemot STM DFU Device. If this device is showing up, please follow the solution below to delete and uninstall it (Step 1-2):

Note: in step 2, please make sure to delete the driver software for the Guillemot STM DFU device, otherwise, the device will appear again. 

After that, if the LED is still flashing red, blue, and green, please start Task Manager and stop the service PiServiceLauncher. In some cases, the SMT device doesn't show up because of the lack of a driver. In this case, please install "stm_dfu_3040_64.exe" from pitool path "C:\Program Files\Pimax\Runtime\dfudriver".
Next, if you can find a device called STM Device in DFU mode in Device Manager, please try to manually flash the firmware:

Please press the Windows key+R on the keyboard and type CMD to enter it. Then, drag the DfuSeCommand.exe (this file is in the tool DFUupgrade) into the command window and input " 0 ". Next, drag the firmware directly to the window like the picture below.
Finally, press the “Enter” key, then the upgrade will be conducted and finished. 

Please download the tool DFUupgrade from the following link:
Kindly remind: the command line is "DfuSeCommand.exe 0 filename", and the file name is like "c:\123.dfu". Please do NOT update the firmware P2.dfu which is in the installation folder of Pitool. You can contact support to get firmware that works for your headset.