The midi modulator doesn't do anything, and is impossible to map to any midi key or pedal.
To Reproduce
Steps to reproduce the behavior:

1. Open BYOD, load the Wah pedal preset
2. Click learn
3. Click any midi keyboard button or pedal
4. Try to use the pedal to control the wah. For me it has no effect.

Expected behavior
Clicking learn should map to a midi pedal or note, which I can use to make a wah sound.

Desktop (please complete the following information):

• OS: MacOS
• DAW: Garageband
• Version 10.4.11