Hello, @z1435. I'll make sure you can reconnect your credit card after the number has change.

You have to disconnect the credit card and then reconnect it again with the updated details.

Here's how:
 

1. Select Transactions on left navigation bar.
2. Click on the Banking tab.
3. Pick the account you want to update.
4. Hit the Edit icon and select Edit account info.
5. On the Account window, tap Disconnect this account on save.
6. Then select Save and close.
    

Then, reconnect account with the new credit card number:
 

1. Select Transactions on the left menu.
2. Click on the  Banking tab.
3. Pick the Connect Account button.
4. Type in the bank account details.
5. Then select the Connect button.
    

Also, know that it will only download 90 days' worth of transactions. If it doesn't download the needed period, you can manually add transactions using a CSV file.

Here's how:
 

1. Go to the Banking menu and select the Banking tab.
2. Click the blue tile for the account you want to upload the transactions into.
3. Select the Link account dropdown and then Upload from file.
4. Then Browse for the file you downloaded from your bank.
5. In the QuickBooks account dropdown, locate the account you want to upload the transactions into.
6. Follow the onscreen steps to match the columns on the file with the correct fields in QuickBooks.
7. Choose the transactions you would like to import then select Yes.
8. Then select Let's go.
    

For additional details, you refer to this article: Manually upload transactions into QuickBooks Online.

I've also added this following articles for your future help:
 

• Categorize and match online bank transactions in QuickBooks Online.
• Reconcile an account in QuickBooks Online.
   

Please keep me posted if you need anything else, especially on how to manage invoices and purchase orders. I'll be around to help you. Keep safe and happy!