Thank you for contacting us, CK18.
I'm here to help apply the credit to the correct bill in QuickBooks Online.
You'll want to open the bill payment, uncheck the applied credit, then mark the correct one. To do so, let's open the vendor transaction list and perform this process.
Here's how:
- Go to Expenses from the left navigation bar, then Vendors.
- Click the vendor name to open the profile.
- Go to the Transaction list tab.
- Open the bill payment with 20 bills and 10 credits.
- Under Credits, mark the correct ones that applied to the open bills.

- Click Save and close.
I've also added these handy articles for additional information about creating credits and how to apply them to your bills:
Stay in touch if there's anything else you need. Just tag my name, and I'll get back to you.
Thank you and stay safe!