Seems promising, but had no success importing the review body from the standard Shopify Review export.
Hi, I'm Dan from Ryivu. Did you change format of your CSV to correct format of our CSV file before importing? Please check our document from here to know how to import reviews via CSV: https://docs.ryviu.com/en/articles/1789782-import-reviews-from-csv-export-reviews-to-csv-features
Dan from Ryviu.