I'd like to ask if I can check in / bag drop on JL36 flight at SIN but it is not actually the first flight in the PNR ticket?

My full itineray is KUL - SIN - HND (MH-JL). JL36 was not available as a reward flight from SIN however it was from KUL hence the booking.
I'm likely to be at SIN enroute to KUL to start this flight so I'm wondering if it would be possible to bag drop in SIN earlier in the day then fly over to KUL.