Rendering a Spherical Sector

Its done. Here is the code

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Data;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEditor.UIElements;
 
 public class Please : MonoBehaviour
 {
     public int ThetaUpper = 30;
     public int ThetaLower = 40;
     public int PhiUpper = 30;
     public int PhiLower = 10;
     public bool edit = true;
     private int ThetaU;
     private int ThetaL;
     private int PhiU;
     private int PhiL;
     public float size = 0.001f;
     private readonly int res = 2;
     private Mesh mesh;
     private MeshFilter meshFilter;
     public float radius = 5.0f;
     private GameObject[] points;
     private Vector3[] vertices;
 
     // Start is called before the first frame update
     void Start()
     {
         this.gameObject.AddComponent<MeshFilter>();
         this.gameObject.AddComponent<MeshRenderer>();
         meshFilter = this.gameObject.GetComponent<MeshFilter>();
         meshFilter.sharedMesh = new Mesh();
         mesh = meshFilter.sharedMesh;
         Create();
         Assign();
     }
 
     // Update is called once per frame
     void Update()
     {
     }
 
     bool check()
     {
         if (ThetaLower == ThetaL && ThetaUpper == ThetaU && PhiLower == PhiL && PhiUpper == PhiU)
             return true;
         else return false;
     }
     void Assign()
     {
         ThetaU = ThetaUpper;
         ThetaL = ThetaLower;
         PhiL = PhiLower;
         PhiU = PhiUpper;
     }
 
     void Create()
     {
         int index1 = (ThetaLower - ThetaUpper) * 2;
         int index2 = (PhiUpper - PhiLower) * 2;
         vertices = new Vector3[index1 * index2];
         int[,] temp = new int[index1, index2];
         int no = 0;
         for (int i = 0; i < index1; i++)
         {
             float theta = ((0.5f * i) + ThetaUpper) * Mathf.Deg2Rad;
             for (int j = 0; j < index2; j++, no++)
             {               
                 float phi = ((0.5f * j) + PhiLower) * Mathf.Deg2Rad;
                 float x = radius * Mathf.Sin(theta) * Mathf.Cos(phi);
                 float z = radius * Mathf.Sin(theta) * Mathf.Sin(phi);
                 float y = radius * Mathf.Cos(theta);
                 vertices[no] = new Vector3(x, y, z);
                 temp[i, j] = no;
             }
         }
         int[] triangles = new int[(index1 - 1) * (index2 - 1) * 6];
         int triIndex = 0;
         for (int i = 0; i < index1-1; i++)
         {
             for (int j = 0; j < index2-1; j++)
             {
                 triangles[triIndex] = temp[i, j];
                 triangles[triIndex + 1] = temp[i + 1, j + 1];
                 triangles[triIndex + 2] = temp[i, j + 1];
 
                 triangles[triIndex + 3] = temp[i, j];
                 triangles[triIndex + 4] = temp[i + 1, j];
                 triangles[triIndex + 5] = temp[i + 1, j + 1];
 
                 triIndex += 6;
             }
         }
 
         mesh.Clear();
         mesh.vertices = vertices;
         mesh.triangles = triangles;
         mesh.RecalculateNormals();
     } 
 }
 

 

This Works