Hi Akshaya,
You can open most standard system forms by using the ActivateMenuItem method of the Application object in the UI API. All you need to know is the menu ID (which you can get by turning on the System Information option in the View menu and then hovering the mouse over the submenu you want to use in the Modules menu). In the case of the GRPO form, the menu id is 2306:
myApp.ActivateMenuItem("2306");
This will trigger the opening of a new instance of the GRPO form. If you want to populate the form after it has opened then you need to loop through the collection of open forms to find your GRPO form and then use the controls on the form to populate the screen.
Kind Regards,
Owen