Step.1 Add reviews on google.

Add snippet 'th-product-review-seo' and add the below code in the snippet.

{% assign product_schema = product.metafields.product_schema %}
{% if product_schema['th_ratingCount'] > 0 %}
  <span class="resourcesratingssummary" itemprop="aggregateRating" itemscope="" itemtype="">
    <meta itemprop="itemreviewed" content="{{ product.title }}">
    <meta itemprop="ratingValue" content="{{ product_schema['th_ratingValue'] }}">
    <meta itemprop="worstRating" content="1">
    <meta itemprop="bestRating" content="5">
    <meta itemprop="reviewCount" content="{{ product_schema['th_ratingCount'] }}">
{% endif %}

Step.2  Add file for review.

Please add the below code in product-template.liquid.

{% include 'th-product-review-seo' %}

Step.3 Check-in structured data testing tool. You just need to paste here any product URL and click on RUN TEST. You will see the Aggregate ratings there. PREVIEW button to see how it will display on Google.

When you click on the PREVIEW button you will see how it will display after Google will crawl your products.