The Self-Select PIN is a random 5-digit number
that you enter as your electronic signature when e-filing your return. You
can reuse your Self-Select PIN from last year or create a new one to use. It
doesn’t matter which option you choose.
For identification purposes, you need to enter either last
year’s Self-Select PIN or adjusted gross income (AGI).
The IRS requires your AGI for
identity verification.
Please review the following TurboTax
FAQ on locating your previous year's AGI:
https://ttlc.intuit.com/replies/3301618