Roth conversion is being treated by Turbotax as a contribution. How do I correct that as am being assessed a penalty for excessive IRA contribution?

Be sure that you have not entered anything in the Traditional and Roth IRA Contributions section of your return pertaining to the Roth IRA.  

A conversion is not the same thing as a contribution and if you converted a Traditional IRA distribution to a Roth IRA, then entering the Form 1099-R reporting the distribution from your Traditional IRA and answering the follow-up questions to show it was converted is all that is required with respect to the Roth IRA.

If you made the Traditional IRA non-deductible contribution during 2023, then that will be entered as a contribution.