How do I apply a credit memo to an invoice?

When I go to Receive payments I get a list of invoices, but just indicating that a credit is to be applied to one of them seems impossible.

Do I put the amount in the "Amount" field at the top? Or just next to the invoice?

When I check "Apply existing credits" it seems to want to apply all the credits, which I don't want.

Why is this so hard? Why can't I just click on the credit and tell QB to apply it to a specific invoice?

Please note: I am using the Mac Desktop version.