Dual monitors may switch positions or orientation if there is an issue with the connection cable, port, or display drivers. If you have a dedicated graphics card, navigate to the manufacturer's website and install the latest drivers if needed (Geforce for Nvidia or Radeon Software for AMD), then restart your computer. If this issue persists,try swapping out the connection and power cables for the monitors to see if this resolves the problem. Often times a monitor will change position when the monitor is disconnected and reconnected in some way, so it would help to check the cables as the root cause.