Welcome to the QuickBooks Community. I know a way on how to enter the opening balance into your account, QBNewbie1.
Once you already created a credit card account, the option to edit it to enter the opening balance is unavailable. However, you can record it by creating a journal entry to keep you track of your business.
For the steps and details, just check out this article: What to do if you didn't enter an opening balance in QuickBooks Online (QBO) Then, go to Step 2: Create a journal entry section.
To learn more about entering opening balances, you can refer to Enter opening balances for accounts in QuickBooks Online article.
I've got a link here that provides you with articles about managing your bank transactions: Find help with bank feeds and reconciling accounts.
Keep me in the loop if you need a hand with reconciling your accounts or any QBO related. I'm always here to help. You have a good one.
