The initial release usually required iOS 4.3 or higher.
If you previously "purchased" Subway Surfers on your Apple ID, you can sometimes go to the Purchased tab on your device. The App Store may offer to download the "last compatible version" for your OS, though this is less reliable for versions as old as 4.2.1. Quick Comparison of Requirements Minimum Requirement Recommended for Old Devices Modern iOS iPhone 6s or newer Legacy iOS iOS 4.3 or higher (standard) iPhone 3GS / iPod Touch 3+ Android Android 5.1+ 768MB+ RAM
Using older versions of iTunes (such as 12.6 or older) or specialized tools like Sideloadly