you can get transcripts online for the last 6 years or by filing 4506-T (free) for transcripts through the mail or form 4506 (fee) for actual copies through the mail from the IRS
https://www.irs.gov/individuals/get-transcript
https://www.irs.gov/site-index-search?search=4506&field_pup_historical_1=1&field_pup_historical=1
or contact the preparer
if self-prepared online contact the business through their website or get a phone number to call.
if self-prepared on your computer that is the only place, other than the IRS, that a copy would exist, but the app would still need to be installed on your computer to open the file if you did not save it as PDF or another type of readable document.
Turbotax online and the IRS only save returns for 6 years so if the other party follows suit returns 2015 and prior may not be available.
