Once you access MyKNX (your Professional account, not your personal account, more information here), follow this path:
My account > My Applications > Update your KNX Manufacturer profile
In order to see this option in your dashboard, you need to have a MyKNX account linked to the KNX Member that you represent. If you cannot see this option, please contact us via a support ticket and we will gladly assist you.
(see the following screenshot)