Redirect after sending email

1

Hi, i have a bootstrap site, but when i send the email by the contact form the system show me a white blank page (contact.php) with the message “Contact form successfully submitted. Thank you, I will get back to you soon!”, i don’t want this but i want to show the page contact.html.
This is the html code:

        <form id="contact-form" method="post" action="contact.php" role="form">
          <div class="row">
            <div class="col-sm-6">
              <div class="form-group">
                <label for="firstname" class="control-label">Nome</label>
                <input id="firstname" name="name" type="text" class="form-control">
                <div class="help-block with-errors"></div>
              </div>
            </div>
            <div class="col-sm-6">
              <div class="form-group">
                <label for="lastname" class="control-label">Cognome</label>
                <input id="lastname" name="surname" type="text" class="form-control">
                <div class="help-block with-errors"></div>
              </div>
            </div>
            <div class="col-sm-6">
              <div class="form-group">
                <label for="email" class="control-label">Email</label>
                <input id="email" name="email" type="text" class="form-control">
                <div class="help-block with-errors"></div>
              </div>
            </div>
            <div class="col-sm-6">
              <div class="form-group">
                <label for="subject">Oggetto in breve</label>
                <input id="subject" name="subject" type="text" class="form-control">
                <div class="help-block with-errors"></div>
              </div>
            </div>
            <div class="col-sm-12">
              <div class="form-group">
                <label for="message" class="control-label">Messaggio</label>
                <textarea id="message" name="message" class="form-control"></textarea>
                <div class="help-block with-errors"></div>
              </div>
            </div>
            <div class="col-sm-12">
              <button type="submit" class="btn btn-primary"><i class="fa fa-envelope-o"></i> Invia il messaggio</button>
            </div>
          </div>
        </form>

And this is contact.php:

<?php

// an email address that will be in the From field of the email.
$from = 'Demo contact form <email@gmail.com>';

// an email address that will receive the email with the output of the form
$sendTo = 'Demo contact form <email@gmail.com>';

// subject of the email
$subject = 'New message from contact form';

// form field names and their translations.
// array variable name => Text to appear in the email
$fields = array('name' => 'Nome', 'surname' => 'Cognome', 'email' => 'Email', 'subject' => 'Oggetto', 'message' => 'Messaggio'); 

// message that will be displayed when everything is OK :)
$okMessage = 'Contact form successfully submitted. Thank you, I will get back to you soon!';

// If something goes wrong, we will display this message.
$errorMessage = 'There was an error while submitting the form. Please try again later';

// if you are not debugging and don't need error reporting, turn this off by error_reporting(0);
error_reporting(E_ALL & ~E_NOTICE);

try
{

    if(count($_POST) == 0) throw new \Exception('Form is empty');
            
    $emailText = "You have a new message from your contact form\n=============================\n";

    foreach ($_POST as $key => $value) {
        // If the field exists in the $fields array, include it in the email 
        if (isset($fields[$key])) {
            $emailText .= "$fields[$key]: $value\n";
        }
    }


    $headers = array('Content-Type: text/plain; charset="UTF-8";',
        'From: ' . $from,
        'Reply-To: ' . $from,
        'Return-Path: ' . $from,
    );
    
    // Send email
    mail($sendTo, $subject, $emailText, implode("\n", $headers));

    $responseArray = array('type' => 'success', 'message' => $okMessage);
}
catch (\Exception $e)
{
    $responseArray = array('type' => 'danger', 'message' => $errorMessage);
}

// if requested by AJAX request return JSON response
if (!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
    $encoded = json_encode($responseArray);

    header('Content-Type: application/json');

    echo $encoded;
}
// else just display the message
else {
    echo $responseArray['message'];
}

I do not understand what to change to stay on contact.html and do not show the white page with the success message, I’m a beginner.