public function submitForm(array &$form, FormStateInterface $form_state) {
$plugin = $form_state
->get('plugin');
$item_type = $form_state
->get('item_type');
// Execute the submit method on the source plugin controller.
$source_ui = $this->sourceManager
->createUIInstance($plugin);
$source_ui
->overviewFormSubmit($form, $form_state, $item_type);
}