Hello,
I have an Saver award tickets for my wife and I (one PNR) that was purchased using combination miles and cash top up.
Today, I want to change the date which also change from Saver to Advantage. However I can't proceed because the system says I don't have enough miles (that is also the reason why I did cash top up on my original booking

)
I am OK to pay cash top up for this change, but seems that it can't be done online. Is this correct?
My local SQ office will not open until 04 November 2021, and there is no guarantee they will not extend the closure.
Do I have to call SQ office in SIN?