In order to set a profile picture in the game, it will be necessary that your account is linked to a Facebook profile. This way, we can avoid the possibility of inappropriate images being used, as Facebook will be in charge of supervising that the photos comply with the established security rules.
If you do not associate your account with a Facebook profile, you will be assigned a random avatar that cannot be changed.
If you wish to link your account to a Facebook profile, you will need to select the tool icon at the top right-hand corner of the home screen to access the Settings menu. Once there, you will find the "Link to Facebook" button under your username.
We invite you to visit the article: How can I link/unlink a Facebook profile to my account?