while there is no access to the quadcopter itself, only Remote Controller is available. When turned on, beeps and most likely asks to calibrate. But connect to the DJI GO fails. The connection between the application and the control panel disappeared after the connection between the control panel and the quadcopter.

I tried:
change wires
change phones
install old applications
clamp C1, C2, Record

nothing helped.

Hi, we're sorry to know about the situation. I would like to ask if you've managed to update the firmware of your unit? Would it be possible if you could verify to us what mobile devices did you use to possibly connect to your remote controller? What is the version of your DJI GO 4 app? For the mean-time, you may refer to our video tutorial below for firmware update of your drone. Please keep us posted on the latest progress.