Since you didn't publish the page, I'm assuming you just spit out the movieLister string like this {%= movieLister %} This should generate the format for the a tag The same format you use in a for loop, like this:

  

    
  

   {table.Rows[i]["rating"]}

{table.Rows[i]["movieName"]}

There are 2 issues with this HTML for what you want

1. There are two closing div tags without a beginning. This may be a typo, but will cause the browser's rendering engine to get very confused (and may also cause StackOverflow syntax highlighter)
2. Although each link has an id attribute that points to the movie ID, that information is not part of the URL that will be loaded when you click the link because it is not in the href attribute

To solve both problems, I will update the output html so that it looks like this:

 
  

    
  

   {table.Rows[i]["rating"]}
 
{table.Rows[i]["movieName"]}

You should then be able to update the page handler like this (note that I'm using a MacBook and can't verify this ASPX code because .NET Core/5 only uses Razor Pages):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace WebProject
{
    public partial class movie : System.Web.UI.Page
    {
        public string movieLister = "";
        protected void Page_Load(object sender, EventArgs e)
        {
            string id = Request["id"];
            string fName = "contentDB.mdf";
            string tableName = "moviesTbl";

            string sqlSelect = $"select * from {tableName}";
            if (id.Length() > 0)
            {
                sqlSelect += $" where id = {id}"
            }

            DataTable table = Helper.ExecuteDataTable(fName, sqlSelect);
            int length = table.Rows.Count;
            for(int i = 0; i < length; i++)
            {
                movieLister += $"
 {table.Rows[i]["rating"]}
{table.Rows[i]["movieName"]}";
            }
            
        }
    }
}

Important Safety Instructions

The above code just demonstrates how to get the ID. In production, I strongly recommend that you convert it to int or parameterize it to avoid very simple SQL injection attacks.

I also strongly recommend migrating to .NET Core/5 and Razor pages as they make it easier to ask questions like this here and on Google since they are self-contained and easier to post full source code . If you want to learn about the Razor page, Tim Corey on YouTube has great videos for every level