How to replace the open folder LOV in POXPOVPO

Could anyone can help me?

I want to replacet the open folder LOV at form POXPOVPO(Purchase Order Summary) via CUSTOM.pll.

In POXPOVPO  form, when press open folder buttom(left top corner at POXPOVPO) , it will list the folder name which is public.

Now, Ijust want to show the fodler which is created by login user, I tries so many ways, but it is not work.

Could anyone can kindly help me?Thank you.

This is my code at CUSTOM.pll

BEGIN

if name_in('system.cursor_item') = 'HEADERS_FOLDER_PROMPT.FOLDER_OPEN'  

and  event_name = 'WHEN-NEW-ITEM-INSTANCE'  

        and  form_name = 'POXPOVPO' --POXPOVPO=PO Summary