Hi there, margueta.
Cases like this, your client can reach out to their former accountant to ask for the company file password. If your client sends the company file using the Accountant's Copy File Transfer, you can ask them if they remember the password they have created for the Accountant's copy.
On the other hand, your client can use the Automated password reset tool for QuickBooks Desktop if they forgot the QuickBooks Admin password. Once they log in to the software, they can access their company file and send you a copy of it.
You can check out this article for more details about the Automated Password Reset Tool: Use the Automated Password Reset Tool for QuickBooks Desktop.
Feel free to reply to this post if you have more questions.