I highly recommend that, as a PFC, you should not call your Career Management NCO directly. You should ask your Squad Leader or Platoon Sergeant to do this for you. First, they will have a better idea of what your Career Management NCO can do for you, and they may very well know the Career Management NCO. Also, your NCOs should have the contact information.
btw, we all say branch manager, but for enlisted Soldiers, the position is actually called Career Management NCO. Branch Manager refers to the Officer in charge of the shop for the whole career field.