Hello. Sorry to hear about the problem that you are experiencing. Apple has a support article that addresses the very issue you are having. Below, I will list the instructions from the article, as well as a link to the article for future reference.
If you purchased a device with iOS 9 or later that's 32 GB or larger, these Apple apps are already installed:
- Pages
- Numbers
- Keynote
- iTunes U
- iMovie
- GarageBand*
*To download GarageBand for free, you need a device that was activated or purchased on or after September 1, 2014.
The first time you open one of these apps, sign in with your Apple ID. If you forgot your Apple ID, we can help you find it.
If you purchased a device with iOS 9 or later that's 16 GB or smaller, or if you updated your existing device to iOS 9 or later, you can download the apps for free. Follow these steps:
Open the App Store. Scroll down to Quick Links and tap Apps Made by Apple.
Get Pages, Numbers, Keynote, iMovie, GarageBand, and iTunes U for free on your iPhone, iPad, and iPod touch - Apple Supp…
Should you have no efficacy using the above described method, contact Apple Care at 1 (800) 275-2273. If you prefer in-person support, please schedule an appointment at your nearest Apple Store. To locate an Apple retail store and schedule a Genius Bar appointment, please visit http://www.apple.com/retail/ and enter your city, state or zip code. Once you have done so and conduct the search, you will be given a list of stores in your area. Choose a store from the list and and you will be taken to the page for that store, from which you can schedule an appointmen. Best of luck with resolving your issue.