I can help you reconnect your credit card account from QuickBooks Online (QBO).
Beforehand, please be aware that disconnecting a bank or credit account from QBO will remove the uncategorized transactions from the bank feed. However, those that were added, categorized, and reconciled will stay in your account.
Follow the steps below to reconnect your account from your Chart of Accounts:
Go to Transactions.
Select the Chart of Accounts.
Look for the disconnected bank account you want to link again.
Furthermore, Once you've successfully reconnected your credit card account, you can check out these articles for future reference in managing bank transactions and reconciling accounts: