Is it possible to transfer data? My father has been doing some friends tax returns for years. He is getting old and has asked me to take this over. How do I do this?

I can sign in to access the returns under his account, but all of the verification codes go to his email. He will continue to do his own returns but he wants me to take care of his friends. I would like to get their previous years returns under my account to prepare their 2023 returns