Hi,
You can refer MV45AF0K_KUNDEN_PRUEFEN include.
where the given function module has been used and it's a same kind of scanario to update WE partner function.
In this FM, you no need to pass SO no. only the type of object and other parameters.
And if it's VA01, at that time you have to pass xvbpa-updkz = 'I' andfor VA02 it would bexvbpa-updkz = 'U'.
Regards,
Praveer.