WishList Member doesn’t control the upload of an Avatar for members as WordPress handles this.
There is an Avatar option in the Settings > Discussion section of WordPress.
There are services that allow Users to upload an image/Avatar that ties to their email address. Then when that email address is used on a site that accepts these images from these services, the image/Avatar will appear.
Gravatar is one of these services and you can get more info regarding that service on their site: