There is no way to determine from our end where the buyer saves the download to their computer; that is determined entirely by them and their browser settings.
Most computers have a file search/find function, so you might want to familiarize yourself with those to help your buyers use it if necessary. You can use your Seller Admin > Send Free Download Link function to send yourself a link and see what the exact filename of the download would be, so you'll know what filename to tell them to search for on their computer.
