How do I amend my 2020 Federal Return for excess 401k contributions that were NOT returned and won't be?

I indicated in TurboTax on my 2020 return that I would be getting the excess returned on a 1099 the following year. However, employer made a mistake and didn't return by April 15 of this year so now cannot. I can't find where in TurboTax amend my taxes that I can indicate that so I can calculate what I now owe on the excess.