I would like to delete invoices in the QB in 2019, 2020, 2021. I can't delete them because whenever I try to delete them QB ask for the password. What password is need?

It's great to have a fresh presence joining us in the QuickBooks Community forum, srazavi. I can provide details regarding the password requirements for modifying invoices from previous years in QuickBooks.

When you try to edit an old invoice in QuickBooks, the software may ask you to enter a password. QuickBooks locks down closed accounting periods to prevent accidental changes that could affect your financial reports and tax filings. The password is a condition set up by the admin to ensure security measures when a user decides to modify entries or transactions from a closed period. You can set up two options or conditions before closing your books. I'll list the following: 

1. Allow changes after viewing a warning. 
2. Allow changes after viewing a warning and entering a password. 

You may have chosen the second option, which results in the system asking for a password before performing any changes. On that note, we don't recommend performing modifications to the closed period since the accounts are already reconciled. It could have an impact on your books and overall financial data. 

Moreover, if you still want to edit the invoices, I encourage you to seek an accountant's assistance. They can provide personalized accounting advice to ensure you're making the right decision. Also, if you have forgotten the password, you can update it in the Account and settings section. Please note, that only Company or Master Administrator users can edit the Closing date conditions. Refer to the attached image. 

Feel free to comment below if you have more questions regarding managing your invoices or sales transactions in QuickBooks, srazavi. I'm here to help and make sure everything runs smoothly for you. Don't hesitate to get in touch if you need more support. Take care!