How to restrict access by Supplier & site while registering new supplier user

Hi,

I am working on iSupplier Portal, R12.1.3.

While registering a new supplier user, the Supplier User administrator enters the supplier name and specifies the prospective supplier user's email address, first name and last name and clicks on Register. Supplier name is mandatory here. He can further restrict the supplier user by site and contact. But those fields are not mandatory.

We want to make it mandatory that a supplier user administrator must enter the site while registering a new user. How can we do that? Please advise.

Regards,

Pankaj