How to remote control Arduino using an old 2.4Ghz toy remote controller?
You have two options:


Use an nRF24L01+ on the Arduino and dismantle the controller to rip out the innards, replacing them with another Arduino and another nRF24L01+.
Do not use the nRF24L01+, instead, rip apart the car and salvage the receiver from it, then work out how you can wire that to the Arduino.


The car's controller will not talk to the nRF24L01+. Yes, they may be in the same frequency band, but they do not talk the same language. After all, your WiFi is on the same band and that doesn't talk to the car, and your microwave, which is also 2.4GHz, doesn't sit and watch satellite TV all day. As you can see the 2.4GHz band is used by a huge number of devices (the band is actually getting quite crowded) and everything talked to everything else in the same band it would be utter chaos.