How to Become a Psychiatric Nurse PractitionerI

I'd love to become a Psychiatric Mental Health Nurse Practitioner. The only program available to me is Family Nurse Practitioner, so my question is;

Is there a way to specialize in psychiatry as a np, or does one need to choose specialization before entering the program.

I know my question may seem silly, but I don't know any NP at my workplace and information online isn't as clear as I'd like.

Thanks in advance.