Execute world generating script in editor

Hi, i'am dealing with a problem. I am begginer in unity coding and i created a script to generate terrain 2d array, but i don't know how to execute it without running the game (I want to run it in editor) so i can then edit the terrain.

How can I run the script?

Here is the code (I know it could be better but it is only supposed to run once on my high end machine so i don't care mouch about the speed)(Ps.: the code has one big mustake and I will repair it, i need to split new Terrain and setNeighbours to two separate FORs but that doesn't realy affest my question):

 using UnityEngine;
 
 public class TerrainScript
 {
 
     private const int TerrainsSize = 500;
     public Terrain[,] Terrains = new Terrain[TerrainsSize, TerrainsSize];
 
     // Use this for initialization
     void Start()
     {
         for (int y = 0; y < TerrainsSize; y++)
         {
             for (int x = 0; x < TerrainsSize; x++)
             {
                 Terrains[x, y] = new Terrain();
                 if (x == 0 && y == 0)
                 {
                     Terrains[x, y].SetNeighbors(null, null, Terrains[x + 1, y], Terrains[x, y + 1]);
                 }
                 else if (x == 0)
                 {
                     Terrains[x, y].SetNeighbors(null, Terrains[x, y - 1], Terrains[x + 1, y], Terrains[x, y + 1]);
                 }
                 else if (y == 0)
                 {
                     Terrains[x, y].SetNeighbors(Terrains[x - 1, y], null, Terrains[x + 1, y], Terrains[x, y + 1]);
                 }
                 else if (x + 1 == TerrainsSize && y + 1 == TerrainsSize)
                 {
                     Terrains[x, y].SetNeighbors(Terrains[x - 1, y], Terrains[x, y - 1], null, null);
                 }
                 else if (x + 1 == TerrainsSize)
                 {
                     Terrains[x, y].SetNeighbors(Terrains[x - 1, y], Terrains[x, y - 1], null, Terrains[x, y + 1]);
                 }
                 else if (y + 1 == TerrainsSize)
                 {
                     Terrains[x, y].SetNeighbors(Terrains[x - 1, y], Terrains[x, y - 1], Terrains[x + 1, y], null);
                 }
                 else
                     Terrains[x, y].SetNeighbors(Terrains[x - 1, y], Terrains[x, y - 1], Terrains[x + 1, y], Terrains[x, y + 1]);
             }
         }
     }
 }