third party designee

Using the TurboTax online editions you cannot add a third party designee on page 2 of Form 1040 unless you print and mail your tax return.

Using the TurboTax desktop CD/Download editions the third party designee can be added using Forms mode and enter the designee on the Federal Information worksheet.  The federal tax return can be e-filed with the designee entered

Credit to @DoninGA View solution in original post

You have to switch to Forms mode (click Forms in the upper right (left for Mac)) and select the Info Wks. Scroll down until you get to Part V Third Party designee: section. Check the YES box and then you can fill in the name, phone number and any 5 numbers for the PIN.

Old Desktop Screenshot