How to make the player die when health = 0?

Depending on how you structured the game Personally, I would use the update method to check whether the health of the player is less than or equal to zero. If its true, I can play a die animation or I can transfer the game to a Game Over Scene

here's the way i would do it

 //include t$$anonymous$$s at the top of the script
 using UnityEngine.SceneManagement;
 
 
 //On your player class where the health variable is sitting
 
 void Update(){
 if(health <= 0){
 //using the game over scene method 
 SceneLoader.LoadScene("GameOver");
 }
 
 }

You will need a Scene named GameOver for t$$anonymous$$s to work and include it in the player settings. again t$$anonymous$$s depends on your structure and what you want to do when the player dies. Some snippet of your code can really help.