To retrieve your original AGI(adjusted gross income) from your previous year's tax return you may do one of the following:
Contact the IRS toll free via their service center.
Complete Form 4506-T Transcript of Electronic Filing at no cost
Complete Form 4506 Copy of Income tax Return
This is if you have already filed the income before.
If your looking for income from previous work I would recommend contacting that companies HR department and asking for the document W2 if you were employed for the company or the 1099 of you were a contractor/ self employed.
I hope this answers you questions. 🙂
