How can I add a motion clip to the animator state by script?

You can see, that I added a new state with the name "StateEmpty" in the Animator. In the bottom image you see the motion slot. How can I add a motion clip to the animator state "StateEmpty" by script?

What I've programmed so far:

 using UnityEngine;

 public class Testing : MonoBehaviour
 {
     public AnimationClip animationClip;

     Animator animator;
     AnimatorOverrideController animatorOverrideController;

     public void Start()
     {
         animator = GetComponent<Animator>();

         animatorOverrideController = new AnimatorOverrideController(animator.runtimeAnimatorController);
         
         animator.runtimeAnimatorController = animatorOverrideController;
     }

     public void Update()
     {
         if (Input.GetKeyDown(KeyCode.Space))
         {
             // https://docs.unity3d.com/ScriptReference/AnimatorOverrideController.html
             //animatorOverrideController["shot"] = animationClip;

             // ... ?
         }
     }
 }

I really don't know how to access this slot.