In the Chart of Account (COA), you cannot use the existing account with a new account, Ham9. I'll be happy to assist you on how to use the existing account to create a new account.

To create a new account in COA while keeping the existing account, first, save the new account under a different name, then edit its details before merging. Keep in mind that merging is irreversible; all data will transfer to the retained account, and the duplicate will be deleted. If any accounts have reconciliation reports, save them beforehand to ensure all transactions remain reconciled on the merged account.

Here's how to merge the account:

1. Look for the duplicate account (one you won't keep or a newly created account).
2. Press the dropdown in the Action column and choose Edit.
   
   
3. Edit the Account name (Name), and Tax form section (Detail Type) so the duplicate's information exactly matches the one you wish to save or the same details on the existing account. 
4. Click Save and Yes, merge accounts to confirm the action. 

For additional information, you can browse through this reference: Merge duplicate accounts, customers, and vendors in QuickBooks Online.

Furthermore, I'll share this helpful article to learn how to reconcile your accounts and manage your books accurately.

Let us know if you have any additional questions about  your Chart of Account, or any other aspect of QuickBooks. Click the Reply button, and we can continue the conversation.