Automatic gamertag and how to change it?

You need to go to xbox.com snd sign in snd go to settings

You can do so here: https://social.xbox.com/changegamertag

Hi ZuraZura1,

Thanks for the reply! Sounds like you've taken the right step in requesting a Case Review with the Enforcement team.
Should the Gamertag change be upheld, and you are unhappy with the assigned Gamertag and wish to change it, one may purchase a new Gamertag through the standard Gamertag change process as our Ambassadors have indicated. However, the
Gamertag that received the forced change will remain unobtainable. I recommend taking a look at our Enforcement site's tips for creating a Gamertag for future use should you need it: https://enforcement.xbox.com/home/staysafe#topic9.

Since there is no further resolution and in an effort to minimize repetitive answers we will be locking this thread, but if you have any further questions or concerns feel free to come back to the Xbox forum (Do not repost the same question or
thread as that would violate the Xbox Forum Guidelines).

We wish you the best and happy gaming.

It should be returned to normal in about a week because the gamertag isnt exactly an offensive one

Well, I suggest talking to support and checking the Xbox Enforcement website, so you will know exactly what happened, whether it was a mistake or a punishment.