Hello there, jterraz.

I'm here to guide you how to enter the data to your chart of accounts.

First, you can download the historical data of an account via an Excel file. As for deleting an account, you can only deactivate it. The transactions of the inactive account will not reflect on any reports, however the sytem still hold its information.

Here's how to download the historical data:

1. From the Gear icon, select Export Data.
2. Select the reason why you're exporting, then click Continue.
3. On the Reports tab, set the desired date range.
4. Toggle the button under Reports and Lists.
5. Select Export to Excel.

Then, here's how to deactivate anaccount:

1. From the Accounting tab, select Chart of accounts.
2. Locate the account.
3. Under ACTION, click the View register drop-down.
4. Select Make inactive.
5. Select Yes.

Then, you can now import your new Chart of accounts.

Once imported, you can add the historical data to the newly added account. Here's an article as your guide:  Manually upload transactions in QuickBooks Online.

I've also attached an article you can use to reconcile the account in QuickBooks: Reconcile accounts in QuickBooks Online.

Feel free to comment below if you have more questions regarding this or any QuickBooks concerns. I'll be here to help. Have a good one.