The New iTunes: How to "Sync" Apps, Books for Windows, and Ringtones
Changes in the new iTunes - Apple Support
With the introduction of iTunes 12.7, and the removal of the Apps and Books stores from the iTunes lineup (which makes sense, since they are separate stores from the iTunes store), there has been a lot of consternation as to how to manage that media going forward.
APPS
Even thought the iOS App Store is no longer located in the iTunes app on your computer, you can still access it via your iOS devcie and purchase, or re-download past purchases from the App Store on the device (the App Store instructions reflect the way it is done in iOS 11. If you are running iOS 10, once you get the App Store open, click on Updates, then on Purchased at the top - select to view All, or Not on this Phone):
Purchases made via your device, are already automatically downloaded, so once you have purchased it on the device, it will download for you.
"Sync" Apps via iTunes:
But what happens when you need to download a past App purchase that is no longer listed in your "Not on My iPhone" list because it is no longer in the Store, or if you need to restore an older version of an App?
The following instructions will tell you how to "Sync" Apps that are no longer available in the Store, or if you need to restore an older version:
1. On your computer, go to iTunes>Preferences>Advanced: Note Location of ITUNES MEDIA LIBRARY
2. Hook up device to computer with current iTunes
3. Click on Library view so that the sidebar can show your device:
4. Then open Finder and follow the path to get to iTunes Media Library. Click on Mobile Applications, and find the app you want. Manage the size of your two windows (iTunes & Finder) so that you can drag the selected app from the Finder folder to the sidebar. Hover just above the device info until you see a square around the device info. Drop the app there and it will sync to the device immediately.
The support article below illustrates more clearly what to look for once you have dragged an eligible media item to the device so it will be sync'd. This article also has links for how to manually manage other items which are no longer in iTunes such as Books on Windows, and Ringtones. Click on the links to get detailed instructions for each.
BOOKS FOR WINDOWS/RINGTONES/AND EVERYTHING ELSE
Manually manage content on your iPhone, iPad, or iPod touch using iTunes - Apple Support
Thanks,
GB