Bonjour. Mabuhay.

If you need to facilitate a late registration for your birth certificate, these are the requiremenst you will need to bring to the local civil registrar:

If the person is less than eighteen (18) years old, the following
shall be required:
Four (4) copies of the Certificate of Live Birth duly
accomplished and signed by the proper parties;
Accomplished Affidavit for Delayed Registration at the back of
Certificate of Live Birth by the father, mother, or guardian,
declaring therein, among other things, the following:
name of child
date and palce of birth
name of the father if the child is illegitmate and has
been acknowledged by him;
if legitimate, the date and place of marriage of parents; and
reason for not registering the birth within thirty (30)
days after the date of birth

In case the party seeking late registration of the birth of an
illegitimate child is not the mother, the party shall, in addition to
the foregoing facts, declare in a sworn statement the recent
whereabouts of the mother.
Any two of the following documentary evidences which may show
the name of the child, date and palce of birth, and name of mother
(and name of father, if the child has been acknowledged):
baptismal certificate;
school records (nursery, kinder-garten, or preparatory;
income tax return of parent/s;
insurance policy;
medical records; and
others, such as barangay captain’s certification.
Affidavit of two disinterested persons who might have
witnessed or known the birth of the child.

You can find more info at www.citizenservices.com.ph