The MB-339 for MSFS hasn't the autopilot like in the real aircraft.
It is supposed for training and all time manual flight.
The aircraft is equipped with a flight director which indicates what attitude you need to maintain to follow a route o a ILS. The flight director can be used in conjunction with VOR, TACAN o AHRS/GPS signal, you only need to switch between VOR/TAC/RNAV pushbutton located on the right side of the HSI.
The product has also a flight manual, you can download it directly from here: https://drive.google.com/file/d/17IfhjD0qfhSZu0ezhWEWTL7k18dRfTNr/view?usp=sharing
Video tutorial for navigation here: