Tokøta, from the Mastering.com Logic Pro course, shows how to map a hardware knob straight to Arpeggiator parameters using Learn MIDI, turning a static arpeggio into something you can shape live.
Click Learn MIDI, move a knob on your controller, then pick a destination like velocity range or note length. The knob now drives that parameter directly.
Moving the knob while the arp plays gets captured as automation in the performance, so a live tweak becomes an editable part of the track.