if you purchased the software from TurboTax as a download, sign onto your download account here - https://shopping.turbotax.intuit.com/unified/downloads?route=myaccounts&cgcview=downloads
You want to install the program? Where did you buy it? Did you buy the CD or the download? What year?
I bought the CD at Costco. I have it installed on my old computer but my new one does not have a CD port.
Even though you can install it 5 times, it seems you can only use the CD 1 time unless you install it on another computer using the other operating system like Mac. And if you installed from the CD it seems you can not download it from online. You can't do both CD and download. See the info on this FAQ
https://ttlc.intuit.com/turbotax-support/en-us/help-article/product-delivery/bought-cd-computer-cd-drive/L89qXCL4V_US_en_US?uid=ln500dlv
Or try copying the CD to a usb flash drive. See SteamTrains post here
https://ttlc.intuit.com/community/taxes/discussion/why-can-t-i-install-turbotax-on-my-laptop-via-download-after-once-installing-on-pc-via-cd/00/2460054