My credit card was replaced due to fraudulent activity. how do i add the new number to quickbooks without creating a new account?

Pretty simple you want to go to your chart of accounts and identify the credit card accounts that were compromised one at a time. Once you do on the right-hand side of the screen you will see a small pull-down arrow next to the word view register on that credit card you have a new number for. Simply click on the small arrow and select edit. It's there you can put in the new last four digits of the credit card number then save and close. Do not enter a new card on a new line simple replace what you have. I typically like to do come like this: 5678 Chase CC (was 1234)

If the account is disconnected from QBO simply go to the banking screen and reconnect the card once you have updated the credit card name in your chart of accounts.