Can you elaborate on what it is you would like to achieve? It’s not clear what from your question.
In general, you cannot apply an audio effect like a Leslie directly to a MIDI note. Instead, you would apply a Leslie audio effect to the instrument that is triggered by the MIDI note. In your case, the Arturia B3 is trigger by the MIDI note. The Arturia B3 already has the Leslie effect built-in to the instrument.
If you are trying to create the common B3 effect where a Leslie spins faster the longer you hold a note or chord, there are a few different ways to achieve that with the Arturia B3. But again, please tell us exactly what you would like to achieve.