I converted my clients company from QBDT to QBO and now there are some very old Deleted accounts from 20 years ago showing up effecting my reports. How can I fix this?

Thanks for reaching out to the Community, @carmerchristina-. I can walk you through how to fix the deleted accounts that appear in your reports.

Inactive or deleted accounts can appear on your financial reports in QuickBooks Online. It happens if the account in question was still active at that time.

To permanently remove deleted accounts from reports, you can reactivate the account first, then delete it again. Here's how to make sure the account is inactive and how to reactivate it:

1. Select the Chart of Accounts from the Gear icon ⚙.
2. At the top of the Chart of Accounts page, choose the small Gear icon ⚙ then tick the box beside Include inactive.
3. Find the account you want to reactivate, then select Make Active.

The accounts will now appear on the Chart of Accounts page. Follow these steps to delete the transactions:

1. Look for the account you just made active. In the Action column, then click ▼ and select Run Report.
2. Customize the Account QuickReport to all dates, then select Run Report.
3. Select each transaction, then either delete it or move it to a different account.

For more details about this, refer to this article: Delete an account on your chart of accounts in QuickBooks Online.

Furthermore, consider checking out this article that tackles what accounts that can and can't be deleted or deactivated: Manage default and special accounts in your chart of accounts.

Please know that I'm only a post away if you have any other questions or concerns. I'll be more than happy to answer it. Keep safe and have a great day!