Miles expiry are automatically extended for another 6 months just before the expiry.
Are my KrisFlyer miles eligible for extension?
If you have KrisFlyer miles expiring between January 2022 to December 2022, they are eligible for a 6-month extension. This extension will be processed automatically, and no action is required on your part. This means that no miles will expire in 2022, and extended miles will only begin expiring from January 2023.