stick sum wings on it
Simply put, you probably cant. If you are trying to use parts from the car to make an airplane, its going to take a lot more than you think. You only have 2 channels, left/right and throttle. The simplest RC airplane you could make would be to use the motor from the car, gear it down/up if needed, and attach it to a propeller. Use the steering mechanism to control a rudder. Now I have a couple RC planes, and they are all 4, 5 and 6 channels (throttle, rudder, elevator, aileron, gear, and various accessories), so thats the first hurdle. Next you need to find a plane to put everything on. Your best bet would be one of those big foam gliders you can get at the dollar store. Get creative, you need to find the center of gravity, try to keep it in the same place after you add all the electronics. Now pray. I doubt it will work the first time, or second... or tenth. Just keep experimenting. That may have been really confusing, but thats what it would take, plus a little more.
okay, short answer: rewiring. long answer: removing the reciever and rerouting the wires attached to the motors in the car to the proper motor(s) in the plane. long answer simplified: reroute the proper wires.
Be careful, there are special frequencies for plane control, an RC car won't use them,
if tis a cheap car youd need to take the transmitter and the reciever connect the motor ports to your parts on rc plane and then itd be done