Add multiple paragraphs programmatically in an AJAX handler

need to add Paragraph fields programmatically to an entity in an AJAX handler.

This is my AJAX callback:

function myAjaxCallback(array &$form, \Drupal\Core\Form\FormState $form_state)  {
  $paragraph3 = \Drupal\paragraphs\Entity\Paragraph::create([
    'type' => 'media',
    'field_caption' => 'Apart from the included Paragraph types, you can create your own simply by going to Structure -> Paragraphs types.',
  ]);
  $paragraph3->save();

  // Now I need to add $paragraph3 to $form['field_gallery_items']['widget']

  return $form;
}

I need to add the new Paragraph I created to the widget so that when the $form is returned I have added a paragraph.

How Can I do that?