The symbol can not be changed via the interface yet.

<icons>
<icon name="3d-objects" path="icons/icon-3D-Objects.png" />
<icon name="Symbol-i" path="icons/Symbol-i.png" />
<icon name="Symbol-Video" path="icons/Symbol-Video.png" />
</icons>
b) Copy the name of your Icon (not the path) - for example "3d-objects"
c) Paste it inside your location tag at the HotSpot tag --> icon="":
<hotspot text="My 3D Object" scaleH="1.0" distanceH="8.0" pan="62.2359" tilt="-26.3593483" tourHotspot="false" color="" icon="3d-objects" visibility="visible" iconType="auto" spotID="258">
<rotatable3DObject distance="2" lookRadius="15" tiltRadius="15" rotationSpeed="0.15" closeRadius="40" modelIndex="4" modelURL="1_6/3D FARO Scan/radlader_66.obj" shader="0" scale="0.0018" allowXRotation="true" allowYRotation="true" allowZRotation="false" posX="1.5" posY="-1.5" posZ="0.0" rotX="-90.0" rotY="0.0" rotZ="0.0" />
</hotspot>