Search WooCommerce Products in WordPress

Just extend your search form with a hidden input: (notice the last input field)

<form role="search" method="get" class="search-form" action="<?php echo home_url( "https://wordpress.stackexchange.com/" ); ?>">
    <label>
        <span class="screen-reader-text"><?php echo _x( 'Search for:', 'label' ) ?></span>
        <input type="search" class="search-field" placeholder="<?php echo esc_attr_x( 'Search …', 'placeholder' ) ?>" value="<?php echo get_search_query() ?>" name="s" title="<?php echo esc_attr_x( 'Search for:', 'label' ) ?>" />
    </label>
    <input type="submit" class="search-submit" value="<?php echo esc_attr_x( 'Search', 'submit button' ) ?>" />
    <input type="hidden" value="product" name="post_type" id="post_type" />
</form>