If you have booked and paid for your ticket on qatarairways.com, please go to
https://www.qatarairways.com/en/refund-request.html
In all other cases, please contact the office or travel agent where you paid for your ticket.
This office should be shown on your e-ticket receipt.
For further enquiries contact your local offices, contact details can be found in the following link https://www.qatarairways.com/en/worldwide-offices.html