Xbox app change picture?

I have the xbox app and my profile picture is a wolf with a purple background. I just wanted to change mine but don't know how. Can anyone help me?

Ps: Don't have an xbox just use your app for minecraft

If you have the mobile version, you can select and use your own profile picture via the menu "My profile", then "Customize", then "Edit gamer picture" and also via the drop-down menu on "Select user-defined gamer picture".