Need help with obstacles that can kill the player.

I have done this: using System.Collections; using UnityEngine.UI; using UnityEngine;

public class PlayerController : MonoBehaviour {

 public float speed;
 public Text countText;
 public Text winText;
 public Text livesText;

 private Rigidbody rb;
 private int count;
 private int lives;


 void Start ()
 {
     rb = GetComponent<Rigidbody> ();
     count = 0;
     SetCountText ();
     winText.text = "";
     lives = 3;
     livesText.text = "Lives: " + lives.ToString;
 }

 void FixedUpdate (){
     float moveHorizontal = Input.GetAxis ("Horizontal");
     float moveVertical = Input.GetAxis ("Vertical");

     Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);

     rb.AddForce (movement * speed);

     if (lives = 0) 
     {
         player.gameObject.SetActive (false);
         winText.text = "You lose!";
     }
 }

 void OnTriggerEnter(Collider other) 
 {
     if (other.gameObject.CompareTag("Pick Up"))
     {
         other.gameObject.SetActive (false);
         count = count + 1;
         SetCountText ();
     }
     if (other.gameObject.CompareTag ("Avoid")) 
     {
         other.transform.position = new Vector3 (-0.48f, 0.75f, 0);
         lives = lives - 1;
     }
 }

 void SetCountText ()
 {
     countText.text = "Points: " + count.ToString ();
     if (count >= 50) 
     {
         winText.text = "You Win!";    
     }
 }

}

and I'm not sure how to do it properly as it keeps giving me errors in the section about removing a life and replacing the figure at the start.