how to load another user session. What code should I add

<?php # utilities.inc.php - Script 9.3
// This page needs to do the setup and configuration required by every other page.

// Autoload classes from "classes" directory:
function class_loader($class) {
    require('classes/' . $class . '.php');
}
spl_autoload_register('class_loader');

// Start the session:
session_start();

// Check for a user in the session:
$user = (isset($_SESSION['user'])) ? $_SESSION['user'] : null;

// Create the database connection as a PDO object:
try { 

    // Create the object:
    $pdo = new PDO('mysql:dbname=cms;host=localhost', 'root', '');

} catch (PDOException $e) { // Report the error!
    
    $pageTitle = 'Error!';
    include('includes/header.inc.php');
    include('views/error.html');
    include('includes/footer.inc.php');
    exit();
    
}

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<?php # index.php - Script 9.7

// Need the utilities file:
require('includes/utilities.inc.php');

// Include the header:
$pageTitle = 'Welcome to the Site!';
include('includes/header.inc.php');

// Fetch the three most recent pages:
try {
    
    $q = 'SELECT id, title, content, DATE_FORMAT(dateAdded, "%e %M %Y") AS dateAdded FROM pages ORDER BY dateAdded DESC LIMIT 3'; 
    $r = $pdo->query($q);
    
    // Check that rows were returned:
    if ($r && $r->rowCount() > 0) {

        // Set the fetch mode:
        $r->setFetchMode(PDO::FETCH_CLASS, 'Page');

        // Records will be fetched in the view:
        include('views/index.html');

    } else { // Problem!
        throw new Exception('No content is available to be viewed at this time.');
    }
        
} catch (Exception $e) { // Catch generic Exceptions.
    include('views/error.html');
}

// Include the footer:
include('includes/footer.inc.php');
?>

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