All unity3d assets you may download on the link: google drive.
Unity Machine Learning Agents allows researchers and developers to create games and simulations using the Unity Editor which serve as environments where intelligent agents can be trained using reinforcement learning, neuroevolution, or other machine learning methods through a simple-to-use Python API. For more information, see the documentation page.
For a walkthrough on how to train an agent in one of the provided example environments, start here.