How to add a beneficial Owner?

When I set up our seller account, I checked a box to say that not all beneficial owners had been entered, but it never asked me for details of the other beneficial owner.

Amazon are now asking me to add the details of the other beneficial owner but I cannot find any instructions on how to do this, and cannot find this anywhere in the settings.

Can someone please advise where I can add the other beneficial owner details?

Many thanks.