1. Navigate to the WordPress plugin directory of your development installation.
2. Navigate to the ch10-book-review-widget directory and edit ch10-book-review-widget.php.
3. Find the Book_Reviews class and add the following block of code within the class to define the form method:

function form( $instance ) { 
    // Retrieve previous values from instance 
    // or set default values if not present 
    $render_widget = ( !empty( $instance['render_widget'] ) ? 
                       $instance['render_widget'] : 'true' ); 
 
    $nb_book_reviews = ( !empty( $instance['nb_book_reviews'] ) ? 
                         $instance['nb_book_reviews'] : 5 ); 
 
    $widget_title = ( !empty( $instance['widget_title'] ) ?  
                      esc_attr( $instance['widget_title'] ) : 
                      'Book Reviews' );            
    ?>
 
    <!-- Display fields to specify title and item count --> 
    <p> 
        <label for="<?php echo  
                    $this->get_field_id( 'render_widget' ); ?>"> 
        <?php echo 'Display Widget'; ?>             
        <select id="<?php echo 
                     $this->get_field_id( 'render_widget' ); ?>"
                name="<?php echo 
                $this->get_field_name( 'render_widget' ); ?>"> 
            <option value="true" 
                <?php selected( $render_widget, 'true' ); ?>> 
            Yes</option> 
            <option value="false" 
                <?php selected( $render_widget, 'false' ); ?>> 
            No</option> 
        </select>                     
        </label> 
    </p> 
    <p> 
        <label for="<?php echo  
                    $this->get_field_id( 'widget_title' ); ?>"> 
        <?php echo 'Widget Title:'; ?>             
        <input type="text"  
               id="<?php echo 
                    $this->get_field_id( 'widget_title' );?>"
               name="<?php
               echo $this->get_field_name( 'widget_title' ); ?>" 
               value="<?php echo $widget_title; ?>" />             
        </label> 
    </p>  
    <p> 
        <label for="<?php echo  
                    $this->get_field_id( 'nb_book_reviews' ); ?>"> 
        <?php echo 'Number of reviews to display:'; ?>             
        <input type="text"  
               id="<?php echo 
                   $this->get_field_id( 'nb_book_reviews' ); ?>"
               name="<?php echo 
               $this->get_field_name( 'nb_book_reviews' ); ?>" 
               value="<?php echo $nb_book_reviews; ?>" />             
        </label> 
    </p> 
<?php } 

4. Save and close the plugin file.
5. Refresh the Appearance | Widgets administration page and expand the Book Reviews widget instance to see the newly created options.
6. Change the widget options and click on Save to update its configuration: