You can do it from the “Reviews” section of your admin panel. At the end of the review description there is an icon that allows you to edit the review. You can basically edit the “Grade” and the “Text” of the given reviews, in case someone left a wrong or abusive review. You can also add a “Grade” and “Text” to a transaction that is waiting for a review, in case, for example, of a user forgetting to leave a review.
You can also decide to delete the review or block it. If you delete the review, the user will be able to leave another review for this transaction. If you block the review, besides deleting it, the user will not be able to leave another review for this transaction.