So, you can do it with either of the two methods. One is online and the other is an offline method. We will discuss both methods in detail in the following sections.

Change Your Qatar Airways Flight Via The Website:
To do this, you need to perform the following steps:
Go to the Qatar Airways official website.
Then head towards Qatar Airways manage booking section.
After this, you need to enter your flight details in the required columns. You will be asked to enter your flight confirmation number and the last name of the passenger also.
Now, the airline will navigate your booking.
From the list appearing, you need to select the flight you want to change.
Then, hit on the flight change feature.
Now, you can look for the flight availability.
Now, you can select the flight as you wish, and do the necessary procedures.
Once, you do the payment, your Qatar Airways flight is changed.

The passengers must receive the mail from the airline as an update on the Qatar Airways flight change.

Change Your Qatar Airways Flight Via Call:
Yes, dial the Qatar Airways customer service number and change your flight with the airline, it is as simple as that. Follow the steps below:

Call on the Qatar Airways customer service phone number.
Then, you will listen to an IVR.
Follow the instructions carefully, and press the necessary number.
Then, you will be connected to the Qatar Airways live agent.
The live person at the airline will change the light on your behalf.

So if you do not want to land into the long process of a flight change, you can simply call Qatar Airways.
Source: https://manageairlinesbooking.com/blog/how-do-i-talk-to-a-live-person-at-qatar-airways/