While entering your form 1099-R, if you have entered a birth date which makes you older than 70 1/2 in the tax year, TurboTax will ask you if any portion of your distribution was transferred to charity (QCD). Answer Yes to that question and you can then enter the amount transferred to charity.
The code in box 7 of form 1099-R must be 7 and the box IRA/SEP/SIMPLE must be checked.
TurboTax will then reduce the taxable amount by the amount transferred to charity.