you can do that only in the Desktop installed program using Forms Mode. There is no question and answer steps for it. You can assign a third party designee in the desktop version of TurboTax using the Forms Mode.
A user found the New place for 2018
2018 introduces Form 1040 Schedule 6, Foreign Address and Third Party Designee - but I couldn't search for Schedule 6. Instead I searched for foreign address, clicked on Jump to Foreign Address, then clicked on the Forms button to bring up the manual entry form. I then could click on YES and enter my name.
