Please I need help figuring out some issues with a Third person controller.

I recently started using the 3D Game Dev Kit in Unity and I have had problems with switching out my character. I watched countless videos on how to swap my character with the Ellen character and every time I try my character falls halfway through the terrain and the animations are processing according the the animator graph. I made sure to associate the new character to humanoid and the animations as well. I followed several videos step by step and it worked for them instantly and I have tried probably 6 times now and it never works. Please help if you have any pointers as to why the character would fall halfway through the floor. The capsule collider is in good placement and the terrain has the proper mesh components too.

Check to see if the rig settings for the animations are set to humanoid & if they are set to "copy from this avatar," I have seen it where you will have to remap the body parts to the avatar you are using.