Avatars on Gamepedia wikis are controlled by Gravatar, a free website that allows you to tie an avatar to your email address.
Simply visit https://gravatar.com/ and create an account using the same email associated with your Gamepedia account. Once you’ve selected an avatar on Gravatar, it should only take a few minutes for the image to start displaying on your wiki account.
Avatars have to be rated G in order to be displayed on Gamepedia.