All you need to do is set one of the CC modlines' Source to "Tilt". Then when you tilt a key forward the value rises and when you tilt a key back (toward you) the value lowers.
You should also know that with 12 Step all of these settings are "global" — they affect all keys. Aside from MIDI notes, you cannot currently set up different controls on a per key basis. So if you set up this tilt functionality then all keys will be capable of sending that message.
The SoftStep is more suited to programming different functionality per key (if that actually is what you're looking for).
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