Installing App

You cannot install what you already have.

"Open" means it is already on your device.

Use Spotlight search and look for it, see below:

Search with iPad

1. Swipe down from the middle of the Home Screen or the Lock Screen.
2. Tap the search field, then enter what you’re looking for.
3. Do any of the following:

• • Hide the keyboard and see more results on the screen: Tap Search.
  • Open a suggested app: Tap it.
  • Get more information about a search suggestion: Tap it, then tap one of the results to open it.
  • Start a new search: Tap  in the search field.

If the app is showing "open" in AppStore, it should be already installed on your iPad.

Check better if its icon has been moved to a different screen page or "hidden" into a folder.

Regards

Giulio