The rejection code will be on the email you received from TurboTax for the state tax return rejected by the state.
If your 2020 return rejected you will have to mail it now. You might not need to fix it depending on why it rejected since you have to print and mail it. If you need to fix something........
How to fix or finish a return you started online
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/01/26322
If the returns are done you can print them out to mail. If you need to finish them, you need to download the tax data file ending in .tax2020 and open it in the Desktop program for that year. If you paid for the Online version you can ask support for the Desktop download. You will need a full Windows or Mac computer to install it on. Or buy the Desktop program here,
https://turbotax.intuit.com/personal-taxes/past-years-products
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).