I'm here to lend a hand, highgrove.
I can show you the steps on how to post a negative opening balance on your credit card account:
Here's how to complete the process:
However, if you didn't enter an opening balance on your Chart of Accounts, you can see below article for guidance on how to handle it:
What to do if you didn't enter an opening balance in QuickBooks Online.
If you have any follow up questions, please let me know. I'm here for you. Have a great day.