How to create random spawn for an object? (C#)

i need to spawn a prefab i created ( tagged "enemy") across carious random points on the board, (which spans from -20 to 20 on both the x and z axis) I also would like it to spawn in waves so if possible keep the base formatting of the code. code is as follows:

using UnityEngine;
using System.Collections;

public class GameController : MonoBehaviour {
public GameObject hazard;
public Vector3 spawnValues;
public int hazardCount;
public float spawnWait;
public float startWait;
public float waveWait;

 void Start ()
 {
     StartCoroutine (SpawnWaves ());
 }
 
 IEnumerator SpawnWaves ()
 {
     yield return new WaitForSeconds (startWait);
     while (true)
     {
         for (int i = 0; i < hazardCount; i++)
         {
             Vector3 spawnPosition = new Vector3 (Random.Range (-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
             Quaternion spawnRotation = Quaternion.identity;
             Instantiate (hazard, spawnPosition, spawnRotation);
             yield return new WaitForSeconds (spawnWait);
         }
         yield return new WaitForSeconds (waveWait);
     }
 }

}