Setting foot pedal to CC#7 on KK S61 first version

I just acquired an old but very serviceable original first-version S61 Mk1; it works great, doesn’t have much in the way of features (but I don’t need any for my particular use), but I DO need to be able to control MIDI volume with a foot pedal.

I haven’t found a way to change it from its current setting, which seems to be expression rather than volume. Is there a way to set the 2nd pedal to CC7 rather than expression?