Hello,
Inside the AUX Switch Menu are choices for FS1, FS2, and FS3. These will cause the Aux switch to operate just like the onboard footswitches but in the opposite mode that the pedal is in. In other words, If the pedal is in PLAY mode then the Aux switch will operate as if the pedal were in BANK mode, when set to FS1, FS2, and FS3.
In this way you can select presets via the Aux switch.