I listed a product as 'generic' but need to change that to my brand.

I already have the units in the fulfilment centres (with SKU) so I cannot create a new listing.

How can I update the brand from 'generic' to my brand name please?

THANK YOU

If someone created a product listing as a generic brand but the item is my item/brand and I am registered in Brand Registry, can I have that ASIN fixed from generic to the correct brand name?

I recently was approved for Amazon Brand registry for my product. My product already had my logo on the box and product itself, but I created my listing under "generic" because I didn't have my product brand registered at that point. I contacted Seller Support about fixing my brand name, but I was told that it would cause confusion for customers. I provided proof that my product has always had a logo on it and my trademark serial number, but I wasn't able to get anywhere. I also have a GS1 barcode for my product. Please help.