UnassignedReferenceException (Didn't find a solution)

I'm a beginner on unity and I have this problem: UnassignedReferenceException: The variable TEXT1 of Player has not been assigned

And this is my main script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 using UnityEngine.UI;
 public class Player : MonoBehaviour {
 
     public GameObject camcam;
     public GameObject score;
     public GameObject Button;
     public GameObject PANEL1;
     public GameObject TEXT1;
     public GameObject TEXT2;
     public int scoremac;
     public double Ytodie;
     public string NextLVL;
     public string ThisLVL;
 
     public static int pointage = 0;
     void Start() {
         PANEL1 = GameObject.FindWithTag("Panel");
         TEXT1 = GameObject.FindWithTag("txt1");
         TEXT2 = GameObject.FindWithTag("txt2");
         pointage = 0;
         PANEL1.SetActive(false);
         TEXT1.SetActive(false);
         TEXT2.SetActive(false);
         score.GetComponent<Text>().text = "Score: " + pointage;
         Button.SetActive(false);
     }
 
     // Update is called once per frame
     void Update()
     {
         AdjustCam();
         CheckKeys();
         CheckScore();
         CheckifFall();
     }
     bool boff = false;
     void CheckifFall()
     {
         if(boff == false)
         {
             if (gameObject.transform.position.y < Ytodie)
             {
                 StartCoroutine(Timer2());
             }
         }
        
     }
 
     public void OnClick()
     {
         TEXT1.SetActive(true);
         TEXT2.SetActive(true);
         PANEL1.SetActive(true);
         StartCoroutine(LoadLevelsPro());
 
     }
     IEnumerator Timer2()
     {
         
         yield return new WaitForSeconds(1);
         pointage = 0;
         SceneManager.LoadScene(ThisLVL);
     }
 
     IEnumerator LoadLevelsPro()
     {
         Button.SetActive(false);
         yield return new WaitForSeconds(1);
         AsyncOperation loading = SceneManager.LoadSceneAsync(NextLVL);
         while (!loading.isDone)
         {
             yield return null;
         }
     }
 
 
     void CheckScore()
     {
         if (pointage <= scoremac)
         {
             score.GetComponent<Text>().text = "Score: " + pointage;
 
         }
         else
         {
             score.GetComponent<Text>().color = Color.green;
             score.GetComponent<Text>().text = "Victoire!";
             boff = true;
             Button.SetActive(true);
         }
     }
 
     void CheckKeys()
     {
         float mouvHorizontal = Input.GetAxis("Horizontal");
         float mouvVertical = Input.GetAxis("Vertical");
         Vector3 mouvement = new Vector3(mouvHorizontal, 0, mouvVertical);
         gameObject.GetComponent<Rigidbody>().AddForce(mouvement * 120 * Time.deltaTime);
     }
 
     void AdjustCam()
     {
         camcam.transform.position = new Vector3(gameObject.transform.position.x,
           gameObject.transform.position.y + 5,
           gameObject.transform.position.z - 10);
     }
 }

This is an example: