CHANGING MY SURNAME ON MY NSO

Hi po sa lahat .
Mag seek po sana ako ng help. I was born in Japan 23 years ago both of  my parents are filipino. Gamit ko po yung surname ng father ko po but when I went to NSO ang nakalagay is yung surname ng mother ko. Parehas kami ng sister ko. So ang ginagawa po namin is kumukuha na lang kami ng Affidavit every time need ng NSO Birthcertificate na nakalagay dun na my father allows us to used his surname. Hindi naman po sila hiwalay ng mom ko. Pero di sila kasal. Paano ko maayos yung case po namin? I want it na po kasi na mabago na yung NSO namin na nakalagay is ung surname ng father ko.

Please help me po.

Thanks you

you can approach the civil registry office kung saan naka-register, ask for assistance how to rectify your birth certificate.