If you have already booked a flight but cannot fly for some important reason, you may choose to cancel your ticket. Qantas Airways offers passengers cancellation options and it is important to understand Qantas Airways cancellation policy before taking any action to cancel a ticket. You can follow the instructions below:

You can request to cancel your ticket within 24 hours of your flight's scheduled departure time.

If the passenger cancels the flight within 24 hours, no cancellation fee will be charged.

Passengers can also request cancellation if the ticket is refundable.

https://www.cancellation-policy.com/qantas-airlines-cancellation-policy