custom fields required

How can I modify this code having in mind i.e. the custom field with meta key “function_name”?

woocommerce_wp_text_input(
  array(
    'id' => 'special_price',
    'label' => __( 'Wholesaler Price *', 'woocommerce' ),
    'placeholder' => '',
    'desc_tip' => 'true',
    'required' => 'true',
    'description' => __( 'Enter wholesaler price here.', 'woocommerce' )
  )
);

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