Hello, I want to add my brand to my generic listing, how can I do that?

I originally listed my item as generic and now I would like to update it to my trademarked brand.

Please note that changing the brand name of an established ASIN is nearly impossible. I would recommend you to start using the brand name which you intend to trademark in the future now. Also, Amazon generally doesn’t allow the updating of product brands, you are expected to create a new listing.