Navigate to another selection screen

Hello. I have a program to upload files in data base tables using bdc method.I have created module pool programming with a push button name as 'conversions'.When I click on 'conversions' pushbutton, it should navigate to my program selection screen.I have tried

CASE SY-UCOMM.

     CALL SCREEN 1000 STARTING AT 20 8 ENDING AT 60 12.

Help please...I have tried finding out and couldnt find it.