How does Krisflyer handle expiring miles on redemptions?

I have some Krisflyer expiring miles coming up and a lot more miles that are still valid for some time. If I redeemed the amount of miles expiring soon will that use the miles that are expiring soon or start with the still good standing miles balance?

I’m thinking of using the miles by booking a flight, redeeming a voucher or transferring the points elsewhere.