access function and change veriable from URL - php

Question

I want to access this function and change the variable from the URL how can i Do that . i try this to echo something and its work
http://test.local/UUser.php
<?php echo '<p>'. 'Hello Husam' . '</p>'; ?>
but how i can access this function inside UUser.php .
For example i need to change $order = "ASC" to $order = "DESC".
public function getBooks($start = 0, $limit = 2, $order = "ASC")
{
$sql_start = $start * $limit;
$sql_limit = $limit;
$sql_order_by = $order;
$query = "SELECT Library.nameOfBook, userBook.book_id, userBook.user_id FROM loginUser JOIN userBook JOIN Library ON userBook.user_id = loginUser.id AND userBook.book_id = Library.id WHERE loginUser.username=:username ORDER BY Library.nameOfBook $sql_order_by LIMIT $sql_start, $sql_limit";
$statment = $this->db->prepare($query);
$statment->execute([
':username' => $this->username
]);
$result = $statment->fetchAll();
echo "<table id='myTable' border='1'>
<tr>
<th><a id='sorter' href='#'>Books</a></th>
<th>Action</th>
</tr>";
foreach($result as $row){
echo "<tr>";
echo "<td>" . $row['nameOfBook'] . "</td>";
echo "<td>" ."<input type='submit' id='delete".$row['book_id']."-".$row['user_id']."' onclick='deleteBook(this)' name='delete' value='Delete'>" . "</td>";
echo "</tr>";
}
echo "</table>";
echo "";
return count($result);
echo '<p>'. 'Hello Husam' . '</p>';
}