Your card isn't connected to the online banking, @KHuihui.

Merging your credit card accounts can be done in just a few easy steps.

1. Go to Accounting.
2. Select Chart of Accounts.
3. Find one of the credit card account you wanted to merge.
4. Under ACTION, select the View register menu.
5. Click Edit.
6. Enter the name the same as your other credit card account.
7. Select Save and Close.
8. Click Yes.

Here's an article you can read to learn more about merging you accounts: How to merge accounts, customers, and vendors?

You can also read this helpful article in case you wanted to start reconciling your credit card account: Reconcile an account in QuickBooks Online.

I'll be here if you need anything else. Thanks!