Mother's surname to Father's surname

pa help po sana ako kasi yung girlfriend ko po hindi niya alam kung saan pupunta. Lumabas kasi sa birth certificate niya na ang apelyido niya ay apelyido ng kaniyang ina. Hindi pa kasal ang kaniyang magulang noong napa rehistro siya. Ngunit naikasal na ang magulang niya ngayon. Gusto lang po namin malaman kung ano po ang hakbang na gagawin namin. Kasi po sa NSO munisipyo hindi daw gumagana ang NCR nila or something. may ibang paraan po ba para mailakad ito sa legal?
Payohan niyo po kami. Maraming salamat po. Gusto niya pong maging legitimate na apelyido ng papa niya ang gagamitin niya. Mag poproseso kasi siya ng kaniyang pasaporte. God bless po sa mag papayo.

P.S. Balak po naming pumunta sa General Santos City para doon humingi ng tulong.

Birth certificate already registered and child is under the surname of the mother and a Private Handwritten Instrument (PHI) by the father is presented
You can use the surname of the father by applying the provisions of R.A. 9255.

The PHI executed by the father should be the basis in order for you to use the surname of your father. Since the surname being used is the surname of the mother, an Affidavit to Use the Surname of the Father (AUSF) should also be executed with the civil registry office where the birth is registered.

Who Shall File
Father
Mother
Child, if of age
Guardian
Where to File
Civil registry office where the birth of the child is registered.
If born abroad with the Consul of the Philippine Embassy where the child is born.
In cases of children born abroad, the birth certificate, shall be annotated by the PSA.
Supporting Documents
PHI executed by the father
AUSF


Nakita ko lang sa website PSA.gov.ph