The solution is to install an older iOS platform in Xcode, along with the latest. This is not done using the Simulator tool but from Xcode.
Open Xcode
Open Settings
Choose the Platforms tab
Click the + icon to add a new platform
Choose the operating system and version that you need.
After the download finishes, you can create a new simulator from the Simulator tool: File -> "New simulator..." The newly installed OS should be selectable.