1. In the Second Display menu, click Arrange Displays…. System Settings opens at Displays.

  2. Drag the display to where the iMac stands next to your Mac, and let go.

Second Display remembers the position of each display and puts it back the next time that Mac connects, so your windows stay where you left them.

  • To start over, click Forget Remembered Arrangement in Settings › Advanced. Each display then starts where macOS puts it.
  • To let macOS place the display every time, turn off Remember arrangement in the same place.
  • You can make the iMac your main display in System Settings. That choice isn’t remembered: when it disconnects, macOS picks the main display again.