I got you back, @jbally. 

I'm here to help you apply the credit note to your customer's invoice. Before we proceed, let me discuss some information on how you can do this in QuickBooks Online (QBO).

In QBO, you can link a credit note to the invoice by creating an Adjustment note. Below are the steps you can perform:

1. Open your QBO account and select the Plus icon at the top and choose the Adjustment note option.
2. From there, input the needed information and click Save and close.
3. Next, to apply the adjustment go back to the Plus button again and pick the Receive Payment feature.
4. Select the correct name of the customer and from the Credits section, select Adjustment Note.
5. Ensure that the total to pay is correct after applying the Adjustment Note.
6. When done select Save and close.

You can check this article for more details about the process: Create and apply adjustment notes or delayed credits in QuickBooks Online. 

Just in case you'll want to transfer the credit of one customer to another, you can easily do it in QBO by creating a journal entry. Here's the link that contains the detailed instructions: How can I transfer credit from one customer to another?.

I'm always happy to assist you with any follow-up questions you may have regarding managing your customer transactions. Don't hesitate to post again here. Take care always.