How to give a speed to random spawned object?

Hi, how can I give a speed to random spawned object. I have this script:

 using UnityEngine;
 using System.Collections;
 
 public class Spawner : MonoBehaviour
 {
     public float spawnTime = 5f;        // The amount of time between each spawn.
     public float spawnDelay = 3f;        // The amount of time before spawning starts.
     public GameObject[] baloon2;        // Array of enemy prefabs.
 
 
 void Start ()
     {
         // Start calling the Spawn function repeatedly after a delay .
         InvokeRepeating("Spawn", spawnDelay, spawnTime);
     }
     
     
     void Spawn ()
     {
         // Instantiate a random enemy.
         int enemyIndex = Random.Range(0, baloon2.Length);
         Instantiate(baloon2[enemyIndex], transform.position, transform.rotation);
         
         // Play the spawning effect from all of the particle systems.
         foreach(ParticleSystem p in GetComponentsInChildren<ParticleSystem>())
         {
             p.Play();
         }
     }
 }
 
 

This script works fine but objects are spawning but not moving. How can I apply speed to them?