I'd be glad to assist with bringing your missing credit card transactions to QuickBooks Online.
If the lacking transactions are selected, you can manually add it to your account, either Sales receipts or Expenses. After that, deposit those payments so it will show up on your reconciliation page.
But if they're many, I'd suggest importing those data using an Excel CSV (comma-separated values) file or another file that is supported by your bank, then categorize it.
Please make sure that deposits may appear as negative amounts because paying your credit card reduces your balance. You can use a 3 or 4 columns template with Date, Description, Amount, and Credit or Debit.
See the sample screenshot below for your reference:
Here's how to import:
Go to the Banking tab on the left, then click the Link Account drop-down arrow or Upload transactions manually.
Choose Upload a file, then tap Browse.
In the QuickBook Account drop-down, pick your credit card, then hit Next.
Follow the on-screen instructions to complete the process.
Once done, you can now proceed in reconciling your credit card account. Just go to the Accounting tab on the left side, then select Reconcile, and enter the Ending balance. For the detailed steps, visit this article: Reconcile an account in QuickBooks Online.
I've also attached articles that will help you in resolving issues while reconciling and how to print or export a reconciliation report.