Try this first (it's easier)
Follow these instructions from Apple: https://support.apple.com/en-us/HT204088
If that won't work for you (possibly because your version of iOS is older)
You can get to your iTunes purchase history from the iTunes application installed on your computer. (It must be the application on your computer, not the app on your device.)
- From the iTunes main menu, choose either Account >> View Account or Store >> View Account. (Some versions of iTunes have one and some have the other.)
- You may have to first choose Store >> Sign In or Account >> Sign In and sign in if the View Account option is not visible.