If the first time you have created an Xbox Live Gamertag was upon signing into Steam, you would have been presented with the option to change your Gamertag after creation. When you complete the process and sign into Steam, some have observed that they are automatically assigned a newly generated Xbox Live Gamertag that is not the one they chose.
The Xbox Live Gamertag system recently underwent a change and the process is best completed through the website directly.
- In a web browser, navigate to https://social.xbox.com/changegamertag
- Sign into the website using the email address and password that was used to sign in to Halo: The Master Chief Collection (please note, this may not be the same as your Steam account)
- Enter your desired Gamertag in the "Your new Gamertag" text field
- Click "Check Availability"
- If available, click "Change Gamertag"