if(isset($form['field_lab_embed'])){
   $form['field_link_embed']['widget']['format'] = [
    '#type' => 'select',
    '#required' => TRUE,
    '#title' => $this->t("Link format"),
    '#options' => [
        'open' => $this->t("option1"),
        'html' => $this->t("option2"),
    ]
  ];