There are many posts here each year regarding this issue. Unfortunately, the only solutions in TurboTax are either to omit the entry of the prior-year amount or to combine the amounts on a single code-D entry and then ignore the warning about overcontributing. The warning about overcontributing has no effect on your ability to file. Omitting the prior-year amount would be extremely unlikely to affect your tax return since doing so would almost certainly not affect your eligibility for a Retirement Savings Contributions Credit given that the combined deferrals exceed the annual deferral limit.
