Transferring Brand Ownership/Rights to Another Amazon Account?

I had gotten approved to sell under a new brand name for an existing Amazon account. After some discussion, my business partner and I decided to separate for the new business leaving me the sole owner. However, the Amazon account it was approved under also sells products through our shared brand.

I created a new Amazon account, paid the membership, went through all of the verification steps, but now I cannot get Amazon to allow me to sell under this brand name because it already exists. Is there a way to transfer the ownership from one account to another? Amazon only provides copy paste responses about using ‘Generic’ brand name.