I was left off my child's birth certificate as the father due to my absence at hospital. How do I put it on it?

What State and what does the mother say?

How long ago was the child born ?

Also if a fair amount of time has passed since birth then you would go to court and start an action to establish legal parantage. You will be required to take a DNA test and there may be child support involved depending on your time with the child.