FAST does not have built-in pitch-control options because most users of FAST have their own control methods that they want to use. Pitch control can be added through one of several ways:
Customize the Fortran SUBROUTINE PitchCntrl() (requires a recompile of FAST).
Implement pitch-control logic in a Bladed-style DLL controller (requires compiling the DLL).
Implement pitch-control logic in Simulink and run FAST through the Simulink interface (requires access to MATLAB/Simulink).
The various documentation supplied with FAST provides some general guidance for all of these approaches.
Another option would be to take the baseline controller for the NREL 5-MW turbine (implemented as a Bladed-style DLL) and adopt the controller gains (including PI gains) for the specific turbine you are analyzing.