if(isset($_POST['become_host'])) {
    $userId = $_SESSION['user_id'];
    $stmt = $conn->prepare("UPDATE users SET role='host' WHERE id=?");
    $stmt->bind_param("i",$userId);
    $stmt->execute();
    $_SESSION['user_role'] = 'host';
    header("Location:/host/today.php");
    exit;
}