You press edit+A/B side of the crossfader & assign what you want. Each side I hear can have up to 128 different parameters assign to them & their min/max values can be flipped - so some can to start low & go higher when moving left while some start high & get lower.
You also use MIDI learn & there’s 1 shortcut way to assign stuff, but I can’t remember.
Here’s a post on all the videos on the Force marcos I could find at the time awhile back:AKAI Force - #2656 by Poetic-Noise