I reconcile some credit card transactions in errors. How can I un reconcile all my transactions so I can start clean ?

Thanks for sharing your first concern, @matrimon-yahoo-c. I'll be your guide today in unreconciling your transactions. 

In QuickBooks, you can only unreconcile one transaction at a time. I'll show you how: 

1. Go to the Accounting menu, then select the Chart of Accounts tab.
2. Locate the account that has the reconciled transaction, then select View register.
3. Find the transaction. You’ll know it's reconciled when it's marked with an “R” in the checkmark ✔ column.
4. Select the transaction to expand the view, then select the box with the R until it's blank to remove it from the reconciliation. 
5. Select Save, then close the account register.

You can use this article for reference: How to Unreconcile a Transaction or Undo a Reconciliation. 

Should you have lots of reconciled transactions to undo, I'd recommend inviting your accountant to your company to help you undo the entire reconciliation period at once.

Let me know if you have additional concerns. I'll be here to guide you more.