On the poly configure page enable only tracks 3 + 4 for polyphony.
Track 1 + 2 are now mono only. Track 3 + 4 will both work in poly mode if the required voices are available. Voice stealing is described in the manual, there are options to determine how this works.
To trigger polyphonic notes:
On one of the tracks enabled for polyphony place a trig and set the note the usual way. On the Arp page, set a value for “No2” - this is the interval to the 2nd note in the chord. No3 + N04 are used for additional notes.
Peace,
Andy.