A Form 1099-R is entered on the 1099 screen for distributions received. If the 1099-R distribution is being reported on another screen instead, mark the Exclude here; distribution is reported on... check box, under the Additional Information for this Distribution section, located on the bottom left of the 1099-R screen.
This tells the software not to carry the amount from the 1099-R screen, but to carry the 8606/ROTH screen entries to Form 8606 to calculate the taxable amount that flows to Form 1040, line 4b.
For more information on non-deductible IRA contributions, see the Form 8606 Instructions.
In prior years, if the amount is being reported on the 8915-D or 8915-E, the taxable amount will flow to line 5b.