Since iOS development depends fully on Apple development tools (Xcode) and since Xcode is only available for macOS, notably you can only compile iOS applications on a Mac computer. Install the Xcode environment using any standard mechanism:
To translate a Sling project to an iOS project using slingbuild, use the following command:
eqela eqela:slingbuild:r19 buildIos src=myproject
This will generate an iOS Xcode project in directory build/myproject/ios/src. This project you can then open normally in Xcode or otherwise handle as any other iOS application project.