Start by building trust of your hand on your sun's back. Place it on his back and give him a treat, telling him he's a good boy and praising him. Do this a few times so he gets comfy with it. Next when you put your hand on his back turn him a little, but dont just turn him upside down just yet. keep tilting him and praising him each time. whe he gets comfy tilt a bit further and further until you have him on his back. Dont train for more than 15 mins at a time because they can get frustrated with what your doing. Also each time you go to train start off with getting comfy with the hand again so you progress faster by reminding him the hand on his back is ok. Hopes this helps you guys