Have linked a wrong credit card account and reconciled few transactions too. Now we need to reverse all those transactions and de-link that credit card.pls advise.

It's my pleasure to help today, @useroffice5.

To start, we can undo the reconciled transactions. Take note that even small changes can unbalance your accounts. To minimize the impact, you can only unreconciled transactions one at a time. 

I also encourage you to consult your accountant if you're unsure. However, if you know what you need to change, here's how to edit and unreconciled the transaction:

1. Go to the Accounting menu.
2. Choose Chart of Accounts.
3. Look for your credit card account holding the transaction.
4. Select Account history.
5. Click the transaction you want to unreconcile to expand the view.
6. Review the check column. If the transaction is reconciled, you’ll see an “R.”
7. Click the checkbox. Keep selecting it until the box is blank. This removes the transaction from the reconciliation.
8. Choose Save and then close the account register.

Once done, you can disconnect your credit card account connected to online banking.

1. Go to the Banking menu or Transactions menu. 
2. Select the Banking tab.
3. Click the tile for the bank account.
4. Choose the pencil ✎ icon, and then click Edit account info.
5. Select the Disconnect this account on save checkbox. 
6. Once done, click Save and Close.

I've also added these articles that can be handy in the future;

• Connect bank and credit card accounts in QuickBooks.
• Reconcile account in QuickBooks Online.

You're welcome to post again here if you need anything else. I'll make sure to get back to you right away. Have a pleasant day.