HOW TO RESTORE ACCIDENTALLY DELETED OUTLOOK

If you are talking about the actual Outlook app, launch the iOS App Store app and go to the Purchases option and look or search your iOS app purchases for Outlook and attempt to re-download this older version back to your iPad.

If no joy, Microsoft has removed all older versions of its apps from Apple's iOS App Store servers and an older, compatible version of MS Outlook for your iPad is no longer available.

FYI,

These old iPad 2,3, 4, 1st gen iPad Mini models are nearing 8 and 9-years old, now.

As of the beginning of 2019, many, MANY third party app developers are all more quickly and completely dropping older app support for all old 7, 8 and 9-year iPads that are running 2-3 year old and earlier iOS versions.

Third party app developers are removing all of their older, legacy versions of their apps from Apple's App Store servers, now.

Older versions of apps are going to be gone for good, now!

Getting older versions of app for these old iPad models, initially from Apple’s iOS App Store is getting to be very difficult and problematic, now, and will only be getting much worse in the year 2020.

These old iPads are now reaching their complete end of life and support.

Old iPads that can no longer be upgraded/updated will have NO MORE APPS AVAILABLE for initial download, at all, soon, from the Apple iOS App Store, for such old iOS devices in the very near future.

Older versions of apps for older iPads will be completely gone, very soon!

Time to now seriously consider a new or discounted, refurbished iPad from Apple.

Sorry & Best of Luck to You!