I need to group materials and objects in game together // Time sensitive//

So I'm creating a tile map with differents biomes. I can create the map and I can assign materials randomly to the tiles. My problem is that I can't create the biomes they should be around 30 tiles large and only consist of one material. I don't know how I can script that.

This is the script I use to generate the map

 public GameObject HexTilePrefab;
 [SerializeField] int mapWidth = 25;
 [SerializeField] int mapHeight = 12;
 [SerializeField] private string tileTag;
 public float tileXOffset = 0.433f;
 public float tileZOffset = 0.747f;
 public Material[] randomMaterials;
 
  
 void Start()
 {
     CreateHexTileMap();
    
 }

 
 void CreateHexTileMap()
 {
     float mapXMin = -mapWidth / 2;
     float mapXMax = mapWidth / 2;

     float mapZMin = -mapHeight / 2;
     float mapZMax = mapHeight / 2;

     
     for(float x= mapXMin; x < mapXMax; x ++)
     {
         for (float z = mapZMin; z < mapZMax; z++)
         {
             GameObject TempGo = Instantiate(HexTilePrefab);

             if (z % 2 == 0)
             {
                 TempGo.transform.position = new Vector3(x * tileXOffset, 0, z * tileZOffset);
             }
             else
             {
                 TempGo.transform.position = new Vector3(x * tileXOffset + tileXOffset / 2, 0, z * tileZOffset);
             }
             SetTileInfo(TempGo, x, z);
         }
     }
 }

 void SetTileInfo(GameObject Go, float x, float z)
 {
     Go.tag = tileTag;
     Go.name = x.ToString() + ", " + z.ToString();
     
 }

And this is the script I use to apply the materials

 [SerializeField]
 private Material[] _materials;
 [SerializeField]
 private Renderer _renderer;

 public void Start()
 {
     ChangeMaterial();
 }

 public void Reset()
 {
     _renderer = GetComponent<Renderer>();
 }

 public void ChangeMaterial()
 {
     _renderer.material = SelectRandomMaterial();
     
 }
 private Material SelectRandomMaterial()
 {
     return _materials[Random.Range(0, _materials.Length)];
 }

I couldn't find anything on google so I'm hoping you can help me. Thank you in advance.