You cannot delete a review. You (or the buyer) can ask Etsy to remove a review but there are very limited reasons why they would. That review doesn't qualify for removal. What you need to do before you reply (and lock the review in) is contact the buyer and explain to them they have purchased a digital download, not a physical item. Check the order and see if it has been downloaded. If so, tell the buyer they have it and perhaps explain where to find the files. If they haven't, make sure they understand downloads can only be accessed via the browser site, and NOT the app.
