Easy! move on the -x axis 2d game

rite now I have this script that spawns and moves this objects in random directions sideways up down etc all random direction moving, I want to change the script to make the game objects move in 1 direction which would be forward , I believe this would be -x actually im sure of this, it would be -x on the screen . This is 2d game

so how do I make them move forward automatically on the -x axis?

thanks

 using UnityEngine;
 using System.Collections.Generic;
 
 // Starting in 2 seconds.// a projectile will be launched every 0.3 seconds
 
 public class sss : MonoBehaviour {
     public GameObject prefab;
     public Rigidbody2D projectile;
 
     void Start() {
         InvokeRepeating("LaunchProjectile", 1.0f, 11.0f);
         Destroy (gameObject, 3.5f);
     }
 
     void LaunchProjectile () {
 
         Rigidbody2D instance = Instantiate(projectile);
         Destroy (gameObject, 3.5f);
 
         instance.velocity = Random.insideUnitSphere * 5;
     }
 
     void SpawnItem()
     {
         // Instantiate the prefab somewhere between -10.0 and 10.0 on the x-z plane 
         Vector3 position = new Vector3(Random.Range(-3.0f, 4.0f), 0, Random.Range(-3.0f, 3.0f));
         Instantiate(prefab, position, Quaternion.identity);
         Destroy (gameObject, 3.5f);
     }
 
 
 }