The excess that was contributed to the traditional 401(k) needs to be included in the amount on Form 1040 line 1. This is generally done by entering the amount of the excess contribution under Wages & Income -> Less Common Income -> Miscellaneous Income, 1099-A, 1099-C -> Other income not already reported on a Form W-2 or From 1099. Answer Yes to Other Wages Received, answer Yes to Any Other Earned Income, select Other as the source, then enter the excess amount contributed to the traditional 401(k).
