You would have to amend the 2018 tax return using Form 1040-X to add the Form 1099-R.
TurboTax does not support tax year 2018.
If the amended 2018 tax return resulted in a tax refund the refund will not be paid since it after the due date of April 15, 2022 for filing a return with a tax refund.
You can seek out a local tax professional to assist you in amending the 2018 return. If the resultant 2018 amended return has taxes owed then you need to file as soon as possible since penalties and interest will continue to accrue until the taxes are paid.
