Just ignore it until the schedule updates with the flights you want. You only get one 'involuntary change of schedule' change request - no givies backies. Once you make adjustments, that will be your final 'free' change for SQ. You may have to battle them a bit to get this change, but being direct with the redemption agent on what you are asking for and clearly asking for their supervisor approval if necessary. The supervisor piece is necessary if they need to open up equivalent award availability for you - which they will if you ask nice (or assertive) enough.

Note that schedules keep changing.... I've ran into an issue with a changed award, and rebooked after a few months once an updated schedule appeared. I sh*t you not, the day I rebooked, they changed the schedule of the rebooked flight (to be less desirable) and SQ wouldn't allow me a second change in the itinerary (despite them changing the schedule again...)