You need to add some case structures around that "+10" area ...
Make some room in that area and drop down a case structure. Wire up the output of the joystick button to the little green control-box on the case structure. In the TRUE window, put your "+10" in there, in the FALSE case, simply wire the GET, thru the case, into the SET.
To get all 4 buttons to steer it up/down/left/right, you'll need to put more cases within that case.
This image doesn't do what you want to do, but you can see how we are taking buttons 3, 4, and 5 and wiring them into the cases to do different things. And we also are using button 1 to override the joystick throttle to 100%.