I highly recommend not trying to use Strymon's banks, they just cause trouble. There are multiple functions stacked on the buttons, you have to hold two at the same time to get some things to work, etc. It doesn't translate well to control by MIDI. Maybe some people here have figured it out a way to make it work and will chime in here, but my advice is to use Device PC -/+ buttons and avoid the headache altogether.
Just edit a button, set Type to Device PC -, and set Device to Timeline. Do the same for another button, setting Type to Device PC +. Pressing the - button will move down one Strymon preset, and pressing the + button will move up one Strymon preset.