I've written a quick "fix" for the Yotpo plugin to enable using rich snippet markup manually. Take note that this snippet is only for version 1.1.8 of the Yotpo plugin for WooCommerce.

function wc_yotpo_show_rs() {
    global $product;
    $yotpo_settings = get_option( 'yotpo_settings' );
    $id = $product->get_id();
    $title = $product->get_title();
    $product_url = get_permalink( $id );
    $description = addslashes( wpautop( do_shortcode( $product->get_short_description() ? $product->get_short_description() : $product->get_description() ) ) );
    $availability = 'https://schema.org/' . ( $product->is_in_stock() ? 'InStock' : 'OutOfStock' );
    $price = $product->get_price();
    $price_valid = date( 'Y-12-31', current_time( 'timestamp', true ) + YEAR_IN_SECONDS );
    $currency = get_woocommerce_currency();
    $sku = $product->get_sku();
    $app_key = $yotpo_settings['app_key'];
    $url = "https://api.yotpo.com/products/$app_key/$id/bottomline";
    $json = ( get_headers( $url )[0] == "HTTP/1.1 200 OK" ) ? file_get_contents( $url ) : null;
    if ( !is_null( $json ) ) { $data = json_decode( $json ); }
    if ( !is_null( $data ) && $data->status->code == 200 ) {
        $avg = $data->response->bottomline->average_score ?: 0;
        $total = $data->response->bottomline->total_reviews ?: 0;
        echo '
            <script type="application/ld+json">
                {
                    "@context": "http://schema.org",
                    "@graph": [
                        {
                            "@type":         "Product",
                            "name":          "'. $title .'",
                            "sku":           "'. $sku .'",
                            "itemCondition": "http://schema.org/NewCondition",
                            "description":   "'. $description .'",
                            "offers": {
                                "@type":           "Offer",
                                "url":             "'. $product_url .'",
                                "availability":    "'. $availability .'",
                                "price":           "'. $price .'",
                                "priceCurrency":   "'. $currency .'",
                                "priceValidUntil": "'. $price_valid .'"
                            },
                            "aggregateRating": {
                                "@type":       "AggregateRating",
                                "ratingValue": "'. $avg .'",
                                "reviewCount": "'. $total .'"
                            }
                        }
                    ]
                }
            </script>'; }
}

You can use this function with an action (i.e. add_action) to use it in your theme.