Help with the Techne tool

I created a mob with the Techne tool. When I put it inside the Mcreator everything goes perfect but when I open the Game and spawneo the Mob turns his head but not the ears, I saw a tutorial in which the model of the ears and head was placed in a "piece" when I put them inside this the position of these is changed and the ears are seen inside the head and I can not move them, help !!