If you have bought TurboTax Desktop, you will be asked for the licence code (installation key) while you install the software, just after it asks you to login.

Once TurboTax Desktop is fully installed, an icon should appear on your desktop. If not, you can search for it in the Start menu, then right click on the icon and select "Open File Location". Then it will pop up a folder with the icons of any TurboTax Desktop products that you have installed on your computer. You can copy and paste the needed icon from the folder to the desktop.