Show buyer how to withdraw A-to-Z claim

Buyer opened an A-to-Z for non-receipt. Amazon granted it and refunded him. He now wants to withdraw the A-to-Z and has asked me how to do it.

Two questions:

1. How does he withdraw his A-to-Z? What exact steps must he take after logging into his buyer account?

2. If we manage to get the A-to-Z withdrawn, will he keep the Amazon granted refund from my account, or do I get that back and then refund him again?

Thanks in advance for your help with this. 11 years on Amazon, and this is my first A-to-Z claim!