You would need his account and user ID--no one else can access that account.
If you used "his" account to prepare and file the returns they are only stored in his account. They are not linked to your old account.
If he will not provide the information for you to get copies you might want to contact your attorney. Or you can get transcripts from the IRS for free. And you can get actual copies from the IRS for a fee of $43 per return.
https://www.irs.gov/individuals/get-transcript
https://www.irs.gov/pub/irs-pdf/f4506.pdf