How to know what particular Customer that corresponds to Business Partner?

Hi Experts,

I have a requirement in the CRM object that I'm developing right now to get the Customer Number that corresponds to the Business Partner that was inputted in the selection-screen.

The scenario is this, in my BSP application I will have selection-screen wherein there will be two input fields, one for Business Partner ID and one for Product Lines ID and a button. When I input a Business Partner ID in the selection-screen and tick on the button, I should get all the details for a Customer to print it out in a smartforms.

All your help will be very much appreciated.

Thanks and Regards.

Monica.