so basically you just put this into the avatar part of your flair:
background-image: url(insert url here?_RNG);
background-position: 0 0;
background-size: auto 100%;
object-position: 9999px;
"insert url here" is where you put in the url that you make at sites
like these ones. The ?_RNG is something you manually put on the end of the url in order to make the image rotation actually work for avatars on PC.