JL's PNR is not understood by Amadeus-based system. You'll need to select seats either on the JL site or call JL.

AY might be able give you the Amadeaus PNR - or ask the (O)TA you booked with (if any)

In a similar situation (JL code, BA & AY metal) I got the Amadeus PNR from BA and from there on it was easy.