Hello naujoks,
If you want to auto-detect more than one MIDI control (e.g. piston, or Launchpad button) to a given virtual control (e.g. the stepper +1 function), right-click on the virtual control, select 'Adjust MIDI/trigger settings manually ...', and use the 'Auto-detect ...' buttons on the various 'Input N' screen tabs. Those tabs exist to allow multiple inputs to the same virtual control.
For virtual pistons/stops/switches there are two tabs, so you can usually auto-detect at most two MIDI controls to any given virtual control. However, in the specific case of the stepper +1 and -1 functions (since people often like to have more than two MIDI pistons controlling them), there are additional entries in the left-hand list of menu functions on that same screen named 'Registration: stepper: trigger +1 [inp 3/4]' and 'Registration: stepper: trigger -1 [inp 3/4]' to which you can auto-detect another two MIDI controls if needed.