To build an iOS app for the Simulator from the command line, it is essential to have Xcode Command Line tools installed. Once set up, the `xcrun xcodebuild` command can be used, specifying parameters such as the project scheme, project path, and desired configuration, to compile the app for a specific simulator target like an iPhone 6 running iOS 10.2 with a 64-bit architecture. This process involves setting the `XCODE_SCHEME` and `XCODE_PROJECT` variables and can be further explored through resources like Stack Overflow and Apple's developer FAQ. TestRigor supports running tests on iOS 10.2 or later, necessitating apps to be compiled for 64-bit architecture.