Title is pretty self-explanatory, this has been a feature requested for years now in TM², and it's as simple as a button that switches from CAM1 to CAM3 (or CAM2 to CAM3, which already is a thing in TM², but it doesn't allow for CAM1 -> CAM3 in that game), without needing to cycle through all 3 cameras, as proposed by the current "change cameras" button.