First thing to do is go to settings, applications, then scroll to Go4 and select. In Go4 tap on defaults and remove any defaults.
Now while in settings scroll down to Developer Options. (if no developer option then then search Google on how to activative on Android). In developer options, turn on "USB debugging" and further down also turn on in USB configuration "MTP protocol"
Now start go4 app and on first page tap the bars top right and turn on USB debugging.
Close app.
Now connect cable to RC and start RC.
As long as DJI Go4 is only drone app installed (ie no litchi or Drone Deploy etc) then Go4 should invoke with a box asking for permission. Say yes this time only or always if only Go4. Good for restarts in case of app crash.
Good luck.
Note~you can only have one app for drone on a Samsung device. Ie Go4, litchi or Drone Deploy etc. You CANNOT have 2 or more at same time or they will conflict and neither will start or run.
There is one way around it but that's another thread.