Good day, omnyacoustics.

Importing a nested chart of accounts is currently unavailable in QuickBooks. You'll need to manually add the sub-accounts of sub-accounts.

If you're using QuickBooks Desktop, here's how:
 

1. Click Lists at the top menu bar and choose Chart of Accounts.
   
2. From the Chart of Accounts screen, right-click and select New.
   
3. Chose the account type and click Continue.
4. Enter the Account Name, tick the box for Subaccount of and choose the sub-account from there.
5. Hit Save and Close.
   

If you're using QuickBooks Online, see the steps below
 

1. Click Accounting in the left panel and choose Chart of Accounts.
2. From the Chart of Accounts screen, click New.
   
3. Choose the Account and Detail Type.
4. Enter the name of the account in the Name field.
5. Mark the box for Is sub-account.
   
6. Click on Save and Close.

To know more about the chart of accounts in QuickBooks, you scan through the articles below. These will provide you steps on how to edit an account as well as delete them:
 

Create subaccounts in your chart of accounts in QuickBooks Online.
Add, edit, or delete accounts in QuickBooks Desktop.

Feel free to drop me a reply below if there's anything else I can help you with. I'd be more than willing to lend you a hand.