I finally figured this after randomly mucking around in Turbo Tax. From the 2023 software open your 2023 return and then go to "Check E-file Status" at the top and then make sure that it updates to show that all your returns have been accepted. Once that happens, then if you go back to start a new return, and click the option in the middle that says "amend a new return", the software should recognize and pull in your 2023 return.
