In my game you have 2 minutes to finish the whole game and after searching for an answer to my problem I think I should use DontDestroyOnLoad but I can't understand how to use it correctly. Here's the code:

public class countdownTimer : MonoBehaviour {

    public float myTimer = 120;
    public Text timerText;
    private bool timerIsActive = true;

    void Start () {
        timerText = GetComponent<Text> ();
    }
    
    void Update () {
        if (timerIsActive) {
            myTimer -= Time.deltaTime;
            timerText.text = myTimer.ToString ("f0");
            print (myTimer);

            if (myTimer <= 0) {
                myTimer = 0;
                timerIsActive = false;
                SceneManager.LoadScene ("lose");

            }
        }

    }
}