EWC+ added new Bank of America account with duplicate transactions

I would use this process to merge the missing transactions from the old account to the new one, and then delete the old account:
https://community.quicken.com/discussion/comment/17263538

Note that if you have attachments they will not transfer using the above method.  If that matters to you the other way to do this is to use multiple select and the menu item to change all the reconcile statuses to C instead of R, then use “Move Transactions” instead of “Copy Transactions”, and then change all the reconcile statuses back.

The reason this is needed is because they have never fixed the bug in Move Transactions that prompts for every single transaction when the reconcile status is R.

Note with this second procedure you will still have the prompt for every transfer transactions where the other side of the transfer has a reconcile status of R.