Countdown.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using TMPro;

public class CountDown : MonoBehaviour
{
    public float InstantiationTimer = 2f;
    public float interval = 2f;
    public int count = 0;

    void Update()
    {
        CreatePrefab();
    }

    void CreatePrefab()
    {
        InstantiationTimer -= Time.deltaTime;
        if (InstantiationTimer <= 0)
        {
            this.gameObject.GetComponent<TextMeshPro>().text = Convert.ToString(count++);
            InstantiationTimer = interval;
        }
    }
}