I recently bought a rc10b4.1 and I noticed it has an AUX button on the transmitter. What is that for? How do I use the AUX button and is there any setup required to use it?

its for a 3RD channel for a servo for reverse like on a monster truck. so you do not need it. i am not sure on tha tradio how to program it for use,unless its already programmed and ready for use.