With Numpad / (division) key. It toggles the RCS mode between Rotation (Pitch, Yaw and Roll) and Translation (Move vehicle up/down, left/right and forward/backward). You really should read the official Orbiter manual (Doc\Orbiter.pdf).
Pretty much all the vessels in Orbiter maneuver the same way. All on the NumPad: Translation: 6-forward-speed up, 9-backward-slow down, 8-down, 2-up, 1-left, 3-right; Rotation: 6-roll right, 4-roll left, 8-pitch down, 2-pitch up, 1-yaw left, 3-yaw right. / switches back and forth, the vessel will tell you what you switch to. Dragonfly has no main engines, retros or hover, just the RCS. It’s designed only for moving modules locally, not for long hauls.