Edit: sorry, miss read your post.
If you allowed the camera app to create the AR Emoji shortcut, open that up and long press on your avatar and select the minus icon to delete it. It will prompt you to delete data for other apps, such as messenger.
If you dont have the shortcut, open up you camera app and find the AR Emoji settings and do the same as above. (I found mine under the More settings in the camera app)