As long as an app you deleted from your iPhone is still available on the App Store, it is possible to reinstall it on your device. The list of your deleted apps is accessible through the App Store on your iPhone running iOS 8.3 or version 12 of the iTunes program on your computer. Each deleted app on the list has a download option that facilitates the reinstallation process.
To view your list of deleted apps, you must sign in to your Apple account on iTunes or the App Store with the same Apple ID you used to download the apps.
Use Your iPhone
Select the App Store icon on your iPhone's Home screen to launch the App Store.
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Tap the Updates icon on the bottom menu bar to open the Updates screen and then tap Purchased.
Tap Not On This iPhone to display your list of deleted apps. Scroll down the list until you find the app that you want to reinstall and then tap the app's Download icon resembling an arrow exiting a cloud.
Wait for the app to install and then launch the app by tapping its Open button.
Alternatively, launch the downloaded app from your iPhone's Home screen by tapping the app after the installation process completes.
Another way to reinstall a deleted app on your iPhone is to find the deleted app in the App Store. Open the App Store, perform a search for the app using the Store's Search function and then tap the app's Download icon.
Use the iTunes Program
Connect your iPhone to your computer and open the iTunes program. Click your name on the menu bar and then select Purchased from the drop-down menu.
If you are not already signed in to your Apple ID account on iTunes, click Sign In on the menu bar and then enter your Apple ID credentials.
Click the Apps tab, select the Not In My Library button and then click the iPhone button to view your list of deleted iPhone apps. Click the Download icon at the upper right corner of the app that you want to reinstall.
Enter your Apple ID password in the pop-up box's Password field and then click the Get button to download the app to iTunes.
Click the iPhone icon on the menu bar at the upper left corner of the window to display the iPhone window. Click Apps under Settings in the window's left pane and then click the Install button next to the app in the Apps box.
Click the Apply button at the lower right corner of the window to sync your iPhone with iTunes and transfer the deleted app to your iPhone.
Update iTunes to the latest version before downloading and syncing the deleted app to your iPhone. Launch iTunes, press the Alt key, open the Help menu and then select Check For Updates.