On Which form do I add the IP Pin?

To enter, edit or delete a 6 digit IP PIN

Click on Federal Taxes (Personal using Home and Business)
Click on Other Tax Situations
Scroll down to Other Return Info
On Identity Protection PIN, click the start button

The IP PIN (Identity Protection PIN) is a 6-digit number that the IRS provides to taxpayers to validate their identity.

Follow the instructions in the TurboTax article How do I add or remove my 6-digit IP PIN? to enter your IP PIN in the correct spot.