Random platform spawning with current code?

Hey Guys, I found a tutorial that shows you have to spawn platforms but the code during the tutorial wasn't explained properly. So what im trying to do is have a list of prefabs that spawns randomly based on condition for example if the score is above 300 then start spawning harder prefabs from the list, i just cant figure out how to do that with the current code. Any help would be appreciated.

 using UnityEngine;
 using System.Collections.Generic;
 
 public class PlatformManager : MonoBehaviour {
 
     public Transform prefab;
     public int numberOfObjects;
     public float recycleOffset;
     public Vector3 startPosition;
     public Vector3 minSize, maxSize, minGap, maxGap;
     public float minY, maxY;
 
     private Vector3 nextPosition;
     private Queue<Transform> objectQueue;
 
     void Start () {
         objectQueue = new Queue<Transform>(numberOfObjects);
         for(int i = 0; i < numberOfObjects; i++){
             objectQueue.Enqueue((Transform)Instantiate(prefab));
         }
         nextPosition = startPosition;
         for(int i = 0; i < numberOfObjects; i++){
             Recycle();
         }
     }
 
     void Update () {
         if(objectQueue.Peek().localPosition.x + recycleOffset < Player.distanceTraveled){
             Recycle();
         }
     }
 
     private void Recycle () {
         Vector3 scale = new Vector3(
             Random.Range(minSize.x, maxSize.x),
             Random.Range(minSize.y, maxSize.y),
             Random.Range(minSize.z, maxSize.z));
 
         Vector3 position = nextPosition;
         position.x += scale.x * 0.5f;
         position.y += scale.y * 0.5f;
 
         Transform o = objectQueue.Dequeue();
         o.localScale = scale;
         o.localPosition = position;
         objectQueue.Enqueue(o);
 
         nextPosition += new Vector3(
             Random.Range(minGap.x, maxGap.x) + scale.x,
             Random.Range(minGap.y, maxGap.y),
             Random.Range(minGap.z, maxGap.z));
 
         if(nextPosition.y < minY){
             nextPosition.y = minY + maxGap.y;
         }
         else if(nextPosition.y > maxY){
             nextPosition.y = maxY - maxGap.y;
         }
     }
 }