Triggering custom chords with a single note from a midi bass controller

I am using Garage Band on my iPad playing live and triggering chords with a single note from a midi bass controller (Studiologic MP-113). Is there any way to trigger a custom chord in this way?

For example, if I have an Em chord that I’d like to replace with Em7 could I add this as a custom chord and trigger it when I play and E (or something) on my midi bass controller?

Thanks in advance!