You were clear enough-- Mark Olson is correct: The Digitech BSW does not have an expression pedal input, therefor can not be controlled by one. Effects need a dedicated control input for expression pedal use, you can't plug into a regular audio jack and get any functionality(with the vast majority of effects anyway. Some effects can take a CV or an audio signal as a modulator, but none share a main audio input as the expression input). Expression inputs in bass/guitar effects use the same 1/4" jacks as audio inputs, but basically are routed to different parts of the pedal internally.
You might try the Boss SYB5 or behringer copy of it if you want a synth pedal with an expression input, where you can control the filter manually with an expression pedal and still have the built in synth sounds underneath, though the SYB's a better 'synth' sound, the tracking isn't near as good,