Setting US Return Address is required if you are selling in the US Amazon.
Please see below to set the return address in Amazon Seller central.
You need to set your return address in seller central when you sell on Amazon.
1. [Seller Account Information] - [Return Address]
2. [Manage Return Address] - [Do you have more than one return address? Manage your return address]
3. [Edit] or [+ Add new address] - Input address (see image) - [Save change]
