Ex girlfriend claimed child without permission

Jessamess366

I have a client that his ex girl friend claimed his son after being broken up over 2 years without his permission (she did claim him once years ago when she was allowed). He now isnt able to claim his son. What route do I tell him to take on this one? He wouldnt have any custody papers with her anywhere as she isnt his mom and they were together for a short time. Dad has son living with him mom is deceased so nothing from the courts as to right of claim but has his birth certificate and social security card. Should he mail them in with a statement and his return?