"The agent suggested that I do two things instead: 1) Input the distribution and any gains on the 1040 line 4a and 4b, and then 2) attach a letter explaining my situation (made excess contribution but removed excess by tax filing due date)"
You accomplish that in TurboTax by entering the contribution under Deductions & Credits, indicating the amount of contribution you requested to be returned, then under Wages & Income entering a 2023 Form 1099-R the same as the one you will receive in January 2024 to show the adjusted amount distributed and any taxable gains. TurboTax will ask you to provide the explanation of the return of contribution.
