how can I add another turbo license code to my existing turbo tax account?

Please explain.  You do not need, nor can you use, more than one license code for 2024 desktop software.   Buying another license code will not give you five more e-files to get past the IRS limit of five.   

Why do you need a second program on the same computer or in your account?   The Desktop program can prepare unlimited returns and efile 5 for free. And you can use any version. All the desktop programs have the same forms. You just get more held in the higher versions.

But you can activate a second program. Under Help - Switch Product - Activate new product. Don't know what that will do or what benefit you will get. Don't think it will allow you to efile more than 5 or get a different free state program.

Or explain more what you are trying to do?