This error usually occurs if the data in the CSV is incomplete/incorrect. Kindly make sure that there is data in the comment_content column of the CSV. If the error is still occurring then please share the CSV file after removoing sensitive data so that we can check it.
We would also like to let you know that this version of the plugin is not currently actively maintained and updated. You may please use the Product Import Export for WooCommerce which supports export/import of reviews and has more features, updates and support.