Display a custom dropdown in single product pages before add_to_cart button

// Display a custom dropdown in single product pages before add_to_cart button
// modify woo-cart file in wordpress for display custom dropdown

function display_dropdown_in_ends_qortechno() {
 if (!(is_product_category() || is_shop()) ) {
	
	 
	echo '<div class="quantity">
	<label class="unit_label" for="id_dropdown_one_end">Unit</label>
        <select id ="id_dropdown_one_end" name="dropdown_one_end">
			<option disabled selected value> - Select a Unit - </option>
            <option value="gal">gal</option>
            <option value="gr">gr</option>
            <option value="Ib">Ib</option>
			<option value="kg">kg</option>
			<option value="mg">mg</option>
			<option value="li">li</option>
			<option value="ml">ml</option>
            <option value="oz">oz</option>
			<option value="sample/MOQ">sample/MOQ</option>
            <option value="ton">ton</option>
			<option value="other">other</option>
	
        </select>
    </div>';
 
}
}
add_action( 'woocommerce_after_add_to_cart_quantity', 'display_dropdown_in_ends_qortechno');

function iconic_add_engraving_text_to_cart_item( $cart_item_data, $product_id, $variation_id ) {
	$cart_item_data['product_unit'] = 'gal';
	return $cart_item_data;
}
add_filter( 'woocommerce_add_cart_item_data', 'iconic_add_engraving_text_to_cart_item', 10, 3 );

add_filter('woocommerce_stock_amount_cart_item', 'custom_woocommerce_update_cart_validation', 10, 2);
function custom_woocommerce_update_cart_validation( $stock, $cart_item_key ){
	$items = WC()->cart->get_cart();
	$cart = $_POST['cart'];
	if( isset( $cart[$cart_item_key] ) && isset( $cart[$cart_item_key]['unit'] ) ){
		global $woocommerce;
		$woocommerce->cart->cart_contents[$cart_item_key]['product_unit'] = $cart[$cart_item_key]['unit'];		
	}
	return $stock;
}

function custom_woocommerce_cart_item_name( $product_name, $cart_item, $cart_item_key ){
	$product_selecton = isset( $cart_item['product_unit'] ) ? $cart_item['product_unit'] : '';
	if( $product_selecton ){
		$product_name .= '<span style="display: block;" class="product-unit">Unit: '. $product_selecton .'</span>';
	}	
	return $product_name;
}
// add_filter('woocommerce_checkout_cart_item_quantity', 'custom_woocommerce_cart_item_name', 10, 3);

add_action('woocommerce_add_order_item_meta','add_product_unit_to_order_item_meta', 9, 3 );
function add_product_unit_to_order_item_meta( $item_id, $item_values, $item_key ) {
    if( ! empty( $item_values['product_unit'] ) )
        wc_add_order_item_meta( $item_id, 'Unit', sanitize_text_field( $item_values['product_unit'] ) );
}

/**
* Remove the Unit from display meta in thank you and email.
*/
function custom_display_item_meta( $html, $item, $args ){
	$strings = array();
	$html    = '';
	foreach ( $item->get_formatted_meta_data() as $meta_id => $meta ) {
		if( trim( $meta->display_key ) !== 'Unit' ){
				$value     = $args['autop'] ? wp_kses_post( $meta->display_value ) : wp_kses_post( make_clickable( trim( $meta->display_value ) ) );
			$strings[] = $args['label_before'] . wp_kses_post( $meta->display_key ) . $args['label_after'] . $value;
		}		
	}

	if ( $strings ) {
		$html = $args['before'] . implode( $args['separator'], $strings ) . $args['after'];
	}
	return $html;
}
add_filter('woocommerce_display_item_meta', 'custom_display_item_meta', 10, 3);