how reassign the hardware buttons with NAVI buttons change other like TomTom app?

Andi feedback to his android car stereo:

Great radio, I'm really satisfied - only the poor media player is not so good. But - it's android, so I can use another one.
BUT - how can I reassign the hardware buttons for "media", "play/pause", "forward" and "backward" ?


 Hi Andi, very sorry for Joying android car stereo just reassign NAVI button,Please find the settings, then find the GPS and choose GPS application to TomTom is OK. Joying android head unit can't reassign the hardware buttons for "media", "play/pause", "forward" and "backward" , Thank you for your support Joying.