Amazon FBA - How to refund a customer

Hello, I’m a Amazon FBA seller.

I would like to fully refund an unsatisfied customer even if he didn’t ask for return or refund.
Is it allowed to do so?

In my order panel, when I click on “Refund order” I have only 2 choices for “reason for refund” :

• Customer return
• General adjustement

Which one should I choose?

Does an FBA seller here already did this kind of refund and have any advice on this ?