What do you need it for? When did they pass? You may need to mail a return for a deceased person so you don't need the AGI. That's only to efile.
How to find the AGI.
https://ttlc.intuit.com/community/agi/help/how-do-i-find-last-year-s-agi/01/25947
Or request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript
