What method directive on a custimized screen

Hello,
how can i find out which method directive i can use for a BPM on a custimized screen? I have the print labels screen which i have customize . i want to use a BPM to autopopulate a customized field with information from the part setup page.

I am having no luck finding the method directive. i tried a trace and got back part whse and part display for the print labels screen.

any help will be appreacited

thanks

Jose