My first issue with a customer

Today I received my first issue in regards to the wrong product being shipped out to a customer. She simply said she received the wrong product and was disappointed. This was amazons fault as they are the ones shipping out and handling my products. So that takes me to my question… What do I need to do on my end? I was going to contact the seller, but I also think Amazon is already taking care of this issue as it shows that I had a product “sold” but it also says I didn’t make any money from it. Anyone that can clarify/help me out on this, please? 🙂