Overview - General Structure: The superknob connects to COMMON Assignable Knobs. These are 8 knobs at the global level. Each of these 8 COMMON Assignable Knobs can, in turn, connect to any Part's (or Parts' ) PART level Assignable Knobs. Each Part (1-16) gets its own set of 8 PART level Assignable Knobs.

Your task would therefore be to find how superknob relates to COMMON and PART level Assignable knobs then find the final destination modulated by a PART Assignable Knob. In this case, the destination of consequence is (Part) "Volume" for each Part you want to change the behavior for.

Detail - Superknob-to-COMMON Assignable Knobs

The easiest way to figure out which COMMON and Part Assignable Knobs are involved in Part Volume is to [EDIT] your Common area. You do this by:

1) Press [PERFORMANCE] (HOME) physical button to return to the home screen
2) Touchscreen - touch the Performance name and then choose "Edit" which will bring you to the Common/Audio editing menus.

3) Navigate to the "Control" -> "Control Assign" menu as seen above. Notice that "Display Filter" has been changed to "Super Knob". This will only show those items Super Knob is assigned to. There will be a list of destinations which will be the various Part Level Assignable Knobs are involved. Note that in the upper-right there is a "Page >" control that may be indicating there are multiple pages of destinations to view. Make sure to go through them all looking for "Volume" under the "Parameter" box. Under "Source" (far left) you will see which COMMON Assignable Knob is tied to Volume. It is important to note the COMMON Assignable knob because we can use this knob to change the direction by reversing its polarity (make it spin the opposite way vs how it currently travels when Super Knob is rotated in a given direction).

4) Once you find your COMMON Assignable Knob which is involved in controlling Volume for the Part that is not working in the direction you want - navigate to the "Motion Control" -> "Super Knob" menu (also under the Common/Audio section) which should show a menu similar to:

Note: it may look slightly different as newer firmware I believe has slightly changed the look. The instructions will be similar.

5) Find the COMMON Assignable Knob that you wish was affecting Volume in the opposite manner. For the sake of example, lets say it was COMMON Assignable Knob #3. In the picture above, you see aligned with Knob #3 is a low value of 0 and high value of 127. Whatever these numbers are, in order to reverse the polarity you would swap the order of these values. For this example I would put "127" in the top box and "0" in the bottom one. Now this knob will spin the reverse direction versus its previous setting when Super Knob is spun in a given direction.

Slight warning: this same knob may be assigned to other destinations. Reversing polarity would reverse polarity for all destinations tied to this COMMON Assignable Knob. I think this would generally be OK (or a non issue due to no other destinations assigned) - but be aware.

Other Way ...

You could also keep the COMMON Assignable Knob spinning in the same direction and, instead, reverse the polarity at the final Parameter itself. This would involve editing the Part and changing the curve. There may be other things to clean up in doing so like reprogramming the initial value.

And Remember ...

[STORE] your edited Performance to save your work.

My advise would be first to locate the proper COMMON assignable knob and reverse its direction rather than dealing with the parameter itself (reversing the curve's ratio) aka "the other way". The rationale here is that there is more cleanup to do by using the destination parameter and curve.

Also the answer was given assuming the starting condition matches the OP's description where the superknob is working for "everything" - just some Part(s) are going in the opposite direction as desired (volume increasing vs decreasing in relationship to rotation of the superknob for a given direction).

As far as the "other way" which involves reversing the curve (or mirroring it so the left-hand side of the curve looks like the right-hand side of the original curve, and vice-versa) - this would make low input values of the controller output values in the opposite way.

There are a few things to consider:

1) Not all curves have an easy "mirror". You may have to create your own user curve for the mirror version.
OR (related - and more standard ...)
2) You may need to change to the opposite ratio and this would usually mean also changing the default parameter value. A ramp that starts (on the left hand side) at 0 and then ramps up going right to a high value in a linear fashion. This kind of curve works well with the parameter programmed to 0 and then as you increase the input (move from left to right on the curve) - you are adding to the programmed value of 0. Now if you use a negative ratio - you will be subtracting more and more from the parameter value. So, to adjust, you'd need to change the parameter value to a high value (not 0) to begin with so the negative ratio has something to subtract from. If set at 0, the value is not going to get smaller - 0 is the lowest.

... and this is what I mean by more things to do.

3) The reset condition of curves should be considered. When the SOURCE of modulated value is reset (from recalling the Performance initially - assuming controllers are not set to HOLD) - you need to factor this into the mix. Sometimes adjustments need to be made to consider the reset condition of a given controller.

There are other threads. I've given more detail to some of these concepts (with pictures) before. I'll see if I can dig that up - but the meat is mentioned here at a high level.