I made a clean backdoor Roth contribution this year. My taxes weren't imported. How do I add my basis in line 24? My 2023 basis was incorrect, do I need to amend this?

I'm using the down loaded version and have been able to correctly characterize the contribution and conversion. However, I can't figure out how to get my cost basis on line 24 of form 8606, when I walk through the steps it changes other numbers in my 8606. Additionally, last year we had an account to our taxes, however he didn't put a cost basis for me but I have done conversions for the last five years. Do I just put in my correct number this year or do I need to file an additional form?