Uniform error: Class 'Uniform\Form' not found

I use Kirby3 and installed the uniform for Kirby3, but the message below appears and does not work. Do you happen to know why?
I made contact.php in the controllers folder and also in the templates folder.
Help me!
Thank you.

site > controllers > contact.php

<?php

use Uniform\Form;

return function ($kirby)
{
$form = new Form([
    'name' => [
        'rules' => ['required'],
        'message' => 'Name is required',
    ],
    'email' => [
        'rules' => ['required', 'email'],
        'message' => 'Email is required',
    ],
    'phone' => [
        'rules' => ['required'],
        'message' => 'Phone is required',
    ],
    'inquiring_product' => [
        'message' => 'Inquiring product is required',
    ],
    'product_use' => [
        'message' => 'Product use is required',
    ],
    'quantity' => [
        'message' => 'Quantity is required',
    ],
    'qna' => [
        'message' => 'Q&A is required',
    ],

]);

if ($kirby->request()->is('POST')) {
    $form->emailAction([
        'to' => 'sonahyong@gmail.com',
        'from' => 'sonahyong@gmail.com',
    ]);
}

return compact('form');
};

site > templates > contact.php

  <form action="<?php echo $page->url() ?>" method="POST">
           <input name="email" type="email" value="<?php echo $form->old('email'); ?>">
           <textarea name="message"><?php echo $form->old('message'); ?></textarea>
           <?php echo csrf_field(); ?>
           <?php echo honeypot_field(); ?>
           <input type="submit" value="Submit">
   </form>
        <?php if ($form->success()): ?>
           Success!
        <?php else: ?>
           <?php snippet('uniform/errors', ['form' => $form]); ?>
        <?php endif; ?>

How did you install the plugin? Is the plugin folder present in /site/plugins?

Thank you so much!
The problem has been solved.

I wrote the name of the Plugins folder as plugin.
Thank you very much! :smiling_face_with_three_hearts: