can't change float value from OnTriggerEnter

code when i go in collider Debug shows the text but time is not added :p

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 public class LevelTimer : MonoBehaviour {
 public Text text;
 public float timeLeft = 30.0f;
      void OnTriggerEnter(Collider other) {
     timeLeft += 10f;
          Debug.Log("hit?");
      }
      void Update()
      {
          timeLeft -= Time.deltaTime;
          text.text = timeLeft.ToString("0");
          if(timeLeft < 0)
          {
              
          }
      }
 }