Hi and welcome to Arturia forums.
1. In SCR mode select the Assign tab. Please read section "5.4. Assign Tab" in the manual.
2. In the MIDI section you find there - click the MAP button above SUS (sustain) so it turns yellow.
3. In the Envelope section now draw a modulation amount for the Damping you wan't to use (a yelow marking will appear). Be sure to set the DAMP MODE to the damping version you will use.
Now the sustain pedal will work for the slot that was selected.
4. Deselect the MAP button for the SUS again (So the button is'nt yellow anymore), to go out of SUS assign mode, when you are done.
Please read about the difference between two Dampings and about the TRIG in the ENVELOPE section in the manual page 27 (31 of 63 in the PDF page selector).
Hope this helps.