How to replace default value of field?

I have a custom module.

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This is form_alter function:

 $form('article') = (
    '#type' => 'textfield',
    '#weight' => -1,
    '#title' => t('Search Product from Magento: '),
    '#autocomplete_route_name' => 'magento_drupal.autocomplete',
    '#ajax' => (
      'callback' => '_select_ajax_form',
      // 'wrapper' => 'my_unique_id',
    ),
  );

In the _select_ajax_form function, how can I automatically fill in the data for the field ‘price’ and ‘sku’?

price is Number (integer) and sku is Text (plain, long).