How Do You Assign Midi Control Sources?

Okay, here’s my situation. I just purchased Wavelore’s Pedal Steel Guitar. I have an Axiom Air 49 controller. The instructions for the PSD say I need to assign MIDI control sources for #4 (neck position) and #5 (portamento speed) and they must be continuous.

I have no idea how to do this. The mod wheel is already controlling vibrato (#1) but no clue how to assign #4 and #5.

Can anybody give me a hand with this? Thanks.