The latest info on United Airlines mobile apps
There is an iOS app from United Airlines which will work on your iPhone, iPod, or iPad.
For United Airlines MileagePlus members, you'll be able to manage your account from the app, though using their website will no doubt provide more functionality
The Android apps from United Airlines work with all Android phones and tablets from various manufacturers (Samsung, LG, Google, etc.), and Android Wear watches might also be compatible. As is often the case, the Android app offers the same functionality as the iOS app.
Also take a look at United Airlines's website by clicking here — you should be able to do what you need there.