I have a child out of wedlock and I want to hsve an access to the child ,since me and the mother of the child are not together anymore. And she has another child with someone else and they are still together.

Ok, first where are you at, Japan, India, UK, US, Canada?
This is a international site and it all differs.

Was she married to anyone else when you had the child with her ?

Are you on the birth certificate or have you formally estabished paternity?

I will assume you do not have court ordered visitation?

So in the US, you will file to establish paternity, and set up court ordered visits with the child