Hi there, @meggiekate.

I'd be happy to help you with deleting your bill even if it's already reconciled.

You can unreconcile it by going to the Bank register, manually click R until it's blank, and click Save. Then, delete the bank transaction so that it will be available back on the Banking page. I'd also recommend asking for advice from your accountant to know what is the best thing to do with changing your reconciled bills to expenses. Especially that you're going to do this process with multiple reconciled bills.

This is how it looks like to unreconcile the transaction:

Once done, go to the Expenses menu, locate the Bill transaction, and delete it. Then, create an Expense transaction, enter all the details such as the date, vendor's name, and amount that you've got from the bank register so that it will match the bank transaction.

I've also included this article to know more details about unreconciling an account: Undo or remove transactions from reconciliations in QuickBooks Online.

You may consider checking out this reference for this year-end tasks with QuickBooks: QuickBooks Online year-end guide and checklist.

As always, you're very welcome to tag my name in the comment section if you have other questions. I'd be glad to answer them for you. Happy Holidays!