Any passenger who does not wish to fly with the airline can cancel their ticket and request a refund. However, you should read the Malaysia Airlines cancellation policy to better understand their terms and conditions. Given are a few points from the airline's policy regarding cancellation:

If you cancel your booking within the first 24 hours of purchasing the ticket, the airline will offer a full refund.
The cancellation fee depends on the ticket class and the destination.
Passengers with Flex tickets can cancel their flight and receive a full refund.
Malaysia Airlines allows you to cancel the flight up to 4 hours before the flight.

How do I cancel my Flight Ticket with Malaysia Airlines?
 
There are two quick ways available through which you can cancel the Malaysia Airlines flight ticket. Go through the given information and use the preferred method:

By calling customer service - Make a phone call to the Malaysia Airlines official phone number and get in touch with customer service. Provide the relevant flight details to the executive, and they will immediately cancel the booking.
 
Through the official webpage - Another possible way to quickly cancel your flight with Malaysia Airlines is through the "Manage Booking" section on the official webpage. Write down the "Booking Reference Number" and "Last Name" as mentioned on the ticket. Then, you have to follow the process to cancel the flight ticket.
 
How much is the cancellation fee for a Malaysia Airlines flight?
 
To cancel a Malaysia Airlines flight, you must pay a fee of $75 to $400, depending on the ticket class and destination. If you want to avoid paying these charges, cancel the booking within 24 hours and receive a full refund. You can also reach out to customer service to get information on the correct cancellation fee.