If you already submitted your return, and you have an IP PIN that you need to enter, your return will be rejected. When it is rejected you can enter it then.
If you did not yet submit your return, you will simply need to select the following and enter your IP PIN
- Federal
- Other Tax Situations
- Start next to Identity Protection PIN under Other Return Info
If this is just the regular 5 digit pin it asks for and not the IP PIN the IRS issued to you, then you can just go back through the file section and enter your 5 digits.