Unity/Shooting game/Assets/Scripts/FlyLogic.cs

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

public class FlyLogic : MonoBehaviour
{
    public float speed = 10;
    // Start is called before the first frame update
    void Start()
    {
        this.Invoke("BulletDestroy", 5);
    }

    // Update is called once per frame
    void Update()
    {
        this.transform.Translate(0, 0, Time.deltaTime * speed);
    }

    void BulletDestroy()
    {
        Object.Destroy(this.gameObject);
    }
}