First of all, it is not possible to merge two separate selling accounts on Amazon. However, if you and your friend want to work together to sell on Amazon, you may be able to create a new joint selling account. To do this, you can register a new account using a new email address that is shared between both of you. You will then need to provide the necessary information and documentation to set up the account, including tax identification numbers, banking information, and product listings. Then you can sell on amazon jointly.
It is not possible to merge 2 Amazon accounts. If you want to share an account with your friend you can use business details to get your account opened. The business details can be shared by you and your friend so in this way you both will be selling via same account.
You cannot combine two Amazon accounts. You can open an account using company information if you wish to share it with a buddy. You and your friend can exchange the company information, allowing you both to sell using the same account.