I have a 4 yr old who's dad left back to Mexico when she was 4 months I want to wt domicary custody how do I do that when I have no idea where he's at

You will need to file the Petition for Custody and Child Support and attempt to serve him.  Once you are unable to serve him, you can request a Curator from the Court who will accept service on his behalf.  You will need to pay for the curator directly since its not part of the court fee.  You should serve his "last known address" in Louisiana through the Sheriffs' Department FIRST and only after they fail to serve him, ask for a curator. If you're in the New Orleans area, dont hesitate to call us at The Civil Law Center, LLC at 504-342-4221.