gift-card-add-settings-in-tab.php

<?php
add_action( 'woocommerce_product_data_panels', 'wcpt_gift_card_options_product_tab_content' );

function wcpt_gift_card_options_product_tab_content() {
	// Dont forget to change the id in the div with your target of your product tab
	?><div id='gift_card_options' class='panel woocommerce_options_panel'><?php
		?><div class='options_group'><?php

			woocommerce_wp_checkbox( array(
				'id' 	=> '_enable_gift_card',
				'label' => __( 'Enable Gift Card Product', 'wcpt' ),
			) );

			woocommerce_wp_text_input( array(
		       		'id'          => '_gift_card_price',
		       		'label'       => __( 'Price', 'wcpt' ),
		       		'placeholder' => '',
		       		'desc_tip'    => 'true',
		       		'description' => __( 'Enter Gift Card Price.', 'wcpt' ),
		       ));
		?></div>
	</div><?php
}