My son is not on his daughters birth certificate how does he go about getting excess

He goes to court to affirm his rights as a parent. Those may include child support and visitation. At that time a DNA test may be ordered by the courts and then after receiving orders from the judge he can be involved in his child's life. If he doesn't do this then he faces being at the mothers bidding and may not be allowed to see his child at all.

I assume you meant access (not excess). As cdad said he file in your local Family court for joint legal custody and visitation. The mother may counter file for child support.

A DNA test may be required to affirm paternity or he may just be required to sign an acknowledgement of paternity if the mother affirms him as the father.

ANY question on law needs to include your general locale as laws vary by area.

Being or not being on a birth certificate does not give or take away any rights.

He will need to file for visitation and prove paternity normally by DNA test