The red arrow shows how the rotors must tilt until the cones (circled in purple) containing the engines faces backwards. When the cones are pointed backwards, with rotors are in the front, the miniaturized interstellar engine inside the cone is turned on, and propels the helicopter forward at speeds capable of interstellar. Interstellar travel is nothing to us, it’s like driving a car across a town, and the engines required for it are getting smaller by the year. The Phoenix fighter uses interstellar engines so small, they’re no bigger than a milk bottle.
Yes, all changes between an interstellar Pegasus and a regular Pegasus are under the hood, just use imagination.