My IRA to Roth IRA conversion had non-taxable amounts, but the 1099R form said undetermined and put the whole amount. Where do I adjust?

I had a small amount of non-deductable traditional IRAs. Is that total deducted from the tax I owe for converting my IRA to a Roth.  If so, can I change the amount taxable on your form?  The 1099R was filled in by Vanguard with the total conversion (or is it considered a roll over?), but they also marked the tax undetermined box.   Where is the Form 8606 in turbo tax premier?

Also does the transfer of money in a prior year from a deferred plan change anything?

Thank you.