How to execute a php code on click of a button?

I have a html/php code as shown below which on click of a download button at Line Z downloads a php file. The drop-down list which I have from the select element is:

1. Hi
2. Hello 
3. Good Morning
4. Good Evening

Let us suppose, I have selected Hi from the dropdown list. On hitting download button, php file (hi.php) belonging to Hi dropdown gets downloaded not executed.

<form method="get" action="fr_get.php">
    <h1>Report</h1>
    <select name="report">
        <?php
        foreach ($reports->getReports() as $report) {
            $users = $report->getAll('AllowedUser'); ?>

            <option value="<?= $report->path; ?>"><?= (is_array($users) && in_array('deleted',
                    $users) ? 'DELETED --- ' : '').$report->getFirst('Title'); ?></option>
            <?php
        }
        ?>
    </select>
    <div class="submit"><input type="submit" value="Download"/></div>   // Line Z
</form>

The code inside fr_get.php is

<?php

$db = connect_mysql();

if (!is_admin()) {
    die('Access Denied.');
}

$report = $_GET['report'];

header('Content-type: text/plain');
header('Content-Disposition: attachment; filename="'.basename($report).'"');

readfile($report);

Problem Statement:

I am wondering what changes I need to make in the php code above so that on click of Download button at Line Z, php file should get executed not downloaded.