Guyyssss, I'm in need of help.

I have the Align T-REX 700 Nitro model with a 7 channel JR PROPO XG7 controller. I've assembled and flew it for the initial test flight, just to see it working so hovering it slightly above ground is enough for the time being. Thing is, I'm planning on adding additional servo for FPV and etc.

I'm totally new and this is definitely gonna sound like a noob question so bear with me
How do I actually switch to other remaining/spare channel aside from the rudder, elevator, aileron, and throttle? Been cracking my brain but I still can't figure it out. Hope Sifus in here can help.