Question inverse kinematics with fuse avatar

Hello to everyone. I'm trying to use inverse kinematics with a fuse avatar (rigged in mixamo). Despite my avatar have all the bones when i opened it on blender, when i upload the avatar on unity it has only 3 bones. I need to have separate bones for all the body part so that when it move the hand all the arm move accordingly. How can i solve this problem.

Thank you so much