You need to install, use Ryviu app on your Shopify store, and follow this instruction below to update your reviews on Google search.
Update your product information on My reviews by select products which you want to update information, click on three dots icon, click on Update Product Info
Notice: You cannot update product information if your store has password.
After that, please click on G icon to update your Google reviews structure data.
You can check is it working by copying your product url and paste to Google Structured Data Testing Tool and check?
If you need more help or any question, please let us know.
All the best,