i've tried plugging it into the micro-usb on the screen, on the remote, then I tried the supplied usb - usb, tried that into the screen, into the remote. tried changing the remote between master / slave / off - tried a second remote. flicked the switch on the drone itself to both positions while doing every one of these things.
Under absolutley no combination of things I have tried is the button to update firmware on the drone ever usable. Every firmware update guide I have seen just says 'plug the drone in!'
I am still yet to take my first test flight and the countless issues I am finding with the inspire 2 so far is not making me very confident about it.

Hi, there. Did you try to update your drone through DJI Assistant 2? Please update it from our website: https://www.dji.com/inspire-2/info#downloads