Find the Prefab in the ‘RuneFox/Skeleton/_Prefabs’ folder and drag it onto your scene then onto your avatar so that it becomes a child object of your avatar.
In the prefab Locate the LeftHandTarget and RightHandTarget gameobjects and move them so that they are in or near your avatar’s Left and Right Hands respectively.
Move the HeadTarget so that it is in front of your avatar’s eyes. Ideally it should be at the same level as your avatar’s view position.
This should be all you need to do and you should be able to upload the avatar.