You no longer need a PIN number from last year to electronically file your return. For security purposes, the IRS now requires that you use your 2018 AGI to validate your return in order to Electronically File your return.
If you used TurboTax last year you can view your 2018 AGI by selecting Documents on the left hand side of your screen. Select View Documents from: Select 2018 on the drop down menu.
OR
You can obtain a copy of last year's tax transcript online using IRS link: Transcript
OR
If you have a copy of your 2018 tax return, your AGI is located on line 7.