I Succeeded updating remote for p3p... this is the advice i got from DJI... i think MAYBE the part that made the difference was to MOVE THE JOYSTICK.
Try uninstalling the app and reinstalling, then connect the mobile device to the remote controller via the USB cable. Then go into camera view of the app and move the joysticks and it should advise you to update the firmware on the remote. Also check what version is on the remote control because if it is less than 1.3.2 you cannot update via the app. You can check the About section of the DJI go app to view what your version is. Go to the last icon on the top at the right ( 3 dots), then scroll down to About. Here is a link on other options to updating the remote;
Try uninstalling the app and reinstalling, then connect the mobile device to the remote controller via the USB cable. Then go into camera view of the app and move the joysticks and it should advise you to update the firmware on the remote. Also check what version is on the remote control because if it is less than 1.3.2 you cannot update via the app. You can check the About section of the DJI go app to view what your version is. Go to the last icon on the top at the right ( 3 dots), then scroll down to About. Here is a link on other options to updating the remote;