You cannot. That would have to be done on an amended 2018 tax return. As of this date, the IRS has not issued any revision of the 2018 forms to support that. Because you have 3 years from the due date of the 2018 tax return to amend, I suspect that the IRS will not address that issue until after the 2019 filing season busy time has ended.
Until the IRS issues revised 2018 forms there is no way for TurboTax to add it.