You 'could' talk to TurboTax Customer Support to see if they would let you finish online, but I'm not sure why someone would want to do that. You are welcome to begin a return Online for free if you wish, but there is no obligation to finish it online when the download is a better product, and you already paid for the desktop product.
If not, you can phone TurboTax Support on Monday, and they will place a download in your account.
If you bought a CD at Costco and do not have a CD drive, look to see if there is a piece of paper inside the box that has a telephone number on it where you can request a download.