Hi I just downloaded QuickBooks.I can't find a Credit Note fuction, how do I reverse an invoice?Thanks Louis.

Good to have you here in the Community, Louis.

First, I'll share the steps on how to create a credit note in QBO. Here's how:

1. Click the + New button and select Credit note.
2. Look for the customer's name in the Customer dropdown.
3. Enter the credit note details, such as the date and the amount. 
4. Choose Save and close.

You can also follow these steps on how to apply the credit note to an invoice:

1. Go back to the + New button and select Receive payment.
2. Look for the name of the customer in the drop-down list for Customer.
3. Select the invoice in the Outstanding Transactions section, then check the box for the credit note that you want to apply in the Credits area. 
4. Click Save and close.

These processes are discussed in this article for additional reference: Create and Apply Credit Notes or Delayed Credits in QuickBooks Online.

Second, you can reverse an invoice by deleting it. Just open the invoice and click More at the bottom. Then, select Delete. 

Please note that it will completely delete or remove the transactions from QBO. You can also check out this article for more details. Void or Delete Transactions in QuickBooks Online.

Let me know if you're able to record a credit note. The Community is always here if you need anything else.