Connecting a footswitch* (FS-5U/FS-6/FS-7, sold separately) to the CH SEL jack of the IR-2 enables you to activate the bypass function without switching channels when holding down the pedal switch.
*If you do not have a footswitch, you can connect an audio cable only as an alternative.
When a footswitch is connected to the CH SEL jack, you can use it to switch channels. See "Using an external footswitch to switch between channels" in the IR-2 Owner's Manual for details on footswitch connection and settings.