You can
change your Qatar Airways flight booking by calling a local office in your area at one of the numbers below. Remember, you must have your travel detail ready, such as your booking reference or E-ticket number, passport information, etc. Also you do it by yourself by following the given method:
1. Click on "Manage booking" or "My Trips" on the homepage.
2. Enter the following details to retrieve your booking:
>Your booking reference (PNR) or E-ticket number
>Your last name
3. Click on the Find booking button
4. Click on the Modify flights button
(If the Modify flights option doesn’t appear, your ticket cannot be changed online—you will need to contact the nearest Qatar Airways office).
5. Follow the prompts to select your new flight and pay the fare difference (if any)