Make us the only seller of brand

Hi

We have just had approval from amazon to create our own listings for a particular brand

We have a letter of authority from the brand owner for us to make the listings for their products

We was talking to the brand owner and he asked what we would have to do to make it that only we can sell his brand and no one else on amazon

What do we have to do to be able to do this
How do we request it from amazon

Thanks