To file your tax return electronically, you will need EITHER last year's self-created 5-digit PIN, or last year's AGI (adjusted gross income). Your 5-digit PIN isn't saved anywhere; in this case you can use you AGI instead.
Your 2023 AGI is located within your prior-year tax documents Form 1040, Line 11.
How do I find last year's AGI?
If you cannot locate either of these numbers, you will need to file your return by paper.