Thanks for visiting the Community, @omartin.
I can walk you through the steps for changing the account on your entry in QuickBooks Online.
You need to run the Transaction Detail by Account Report to find the transaction and edit the posting account. Here’s how:
1. Go to Report from the left pane.
2. Enter Transaction Detail by Account on the search box.
3. Locate Petty Cash account and click the transaction.
4. Once it opens, select the right bank on the Account drop-down.
5. Hit Save and close.
Once done, the entry should now post to the right account.
That should answer your question for today. Let me know if you need further assistance working with QuickBooks. I’ll be here to help you out. Take care and have a good one!