In the MicroPitch algorithm, the Flex (Performance) Switch will double the current pitch shift settings in both Pitch A and Pitch B. So, 0, 1, 2, 3, … 49, 50 cents on the PitchFactor jumps to 0, 2, 4, 6, … 98, 100 cents. If a full semitone covers what you’re after, PITCH MIX to A0+B10, PITCH B to -50c, then lock in the Flex switch.
I like to use a latching Aux Switch, tied to the Performance Switch [Pedal -> Aux Switches in H9 Control]. But even a simple TS plug will work in a pinch. Use an Aux Switch setting to TIP, and short the tip and sleeve together on the plug itself. That’s if you want the doubled pitch shift from Flex to stay latched on.