How to use indexers in C#

// Defining Node for Linked List
class Node {  
    public int data;  
    public Node next;  
    public Node(int d) {  
        data = d;  
        next = null;  
    }  
}  
// Defining Linked List
class LinkedList {  
   Node head;  
   // Setting up indexers
   public int this[int i]
   {
      // get indexer allows square brackets to read data
      get => this.getAt(i);
      // set indexer allows square brackets to change data
      set => this.setAt(i, value);
   }
   // Function defined for indexer
   public void setAt(int i, int value)
   {
       int count = 0;
     Node temp = this.head;
     while (i > count){
       if (temp.next != null){
        temp = temp.next;
        count++;
       }
        else if (i != count){
          throw new System.ArgumentException("Out of bound element accessed");
        }
     }
     temp.data = value;
   }
   // Function defined for indexer
   public int getAt(int i)
   {
     int count = 0;
     Node temp = this.head;
     while (i > count){
       if (temp.next != null){
        temp = temp.next;
        count++;
       }
        else if (i != count){
          throw new System.ArgumentException("Out of bound element accessed");
        }
     }
     return temp.data;
   }
   // The following functions give basic functionality
   // to the Linked List
   public void pushBack(int new_data)    
    {    
      Node new_node = new Node(new_data);    
      if (this.head == null) {    
          this.head = new_node;    
          return;    
      }    
      Node temp = this.head;  
      while (temp.next != null) {  
          temp = temp.next;  
      }  
      Node lastNode = temp;    
      lastNode.next = new_node;    
    }    
    public void pop()
    {
      this.head = this.head.next;
    }
}  
class HelloWorld
{
    static void Main()
    {
        // Setting up Linked List
        LinkedList list = new LinkedList();
        list.pushBack(10);
        list.pushBack(20);
        // Accessing data using indexers
        System.Console.WriteLine(list[0]);
        System.Console.WriteLine(list[1]);
        // Changing data using indexers
        list[1] = 15;
        System.Console.WriteLine(list[1]);
    }
}