If I purchased Deluxe Turbotax for 2020 in January and have a license code. Where do I add the code in order to not pay for this a second time?

Are you using the Online version?    Sorry you can't apply the Desktop CD/Download program purchase to the Online version. They are separate prices and work different.

You need to install the program on your computer and move your online return to the Desktop program. You can download the .tax2020 data file without paying for Online and continue in the desktop version see this…….

https://ttlc.intuit.com/community/choosing-a-product/help/how-do-i-switch-from-turbotax-online-to-the-turbotax-software/00/26129

After you get the program installed the first thing to do before you open your tax return .tax file is to update the program and install any state programs you had. Then open your file. So you first might need to start a fake return to be able to download the state program (go to FILE - NEW).