You would need to use the booking reference (PNR) or ticket number. Do note that if you use a voucher this way then you must book a flight of equal or greater value or you will lose the residual value.
You can convert this booking to a gift card that will not expire or Aeoplan miles however expect that to take 6 weeks (or more).
Last edited by dr_torch; Jul 13, 2020 at 5:55 pm