The Product Reviews app is the default review tool offered by Shopify.
To integrate Searchanise widgets with the Product Reviews app you'll need to enable the Product Reviews integration in the Searchanise admin panel.
1. Go to Searchanise admin panel -> Integrations -> Product reviews.
2. Set the toggle for Product Reviews to On.
3. Click Apply changes.
4. Update search results
Go to the Dashboard section in the Searchanise control panel and click Force re-indexation.
After that you'll see review stars and the number of Shopify Product Reviews in Searchanise widgets and you'll be able to filter by reviews as well.