I reported contributions to a Roth IRA rather than Roth 401k. I was penalized for exceeding contribution limits in error - how do I correct for this year and last?

You can correct this by amending your returns.  There's nothing specific on your tax return that needs to be reported for a Roth 401(k) contribution. 

It is too early to amend 2024. Use this tool to check availability of forms, including 1040X: Tax form availability.

You can amend 2023 now. Here is how to do this in TurboTax Online, from How do I amend my federal tax return for a prior year?:

1. On the Tax Home screen, scroll down to Your tax returns & documents and select the year you want to amend.
2. Select the Amend (change) return dropdown, then Amend using TurboTax Online.
3. Continue through the screens, make the changes you need to make (delete the Roth IRA input), and carefully answer the remaining questions to finish amending your return.