I need to unreconcile my bank account, but I can't locate the "UNDO" button referenced in the instructions. I have Quickbooks Basic online?

We appreciate your effort for posting here in the Community, @woodlandskiwanis. Reconciling your accounts is a great practice for managing your finances. Let's work side-by-side to ensure a smooth reconciliation process.
 

Here's how:
 

1. Go to the Accounting menu. Then select Chart of Accounts.
2. Find the account and select View register.
3. To help you focus on this task, filter the register to only include the last 60 days of transactions.
4. Review the check column. If the transaction is reconciled, you’ll see an “R.”
5. Select the box and keep clicking it until it's blank. It removes the transaction from the reconciliation.

Moreover, I've added here an article that will help you in case you encounter reconciliation issues: Fix issues when you're reconciling accounts.

I hope this post finds you well and keep us posted if you have any inquiries about managing your finances in your QuickBooks Online account. We'll be here to provide you guidance 24/7 and ensure you have the best experience with QuickBooks.