Apple default apps

There is no AirDrop app. You access AirDrop from within other apps (and in Settings). See the following for more information: How to use AirDrop on your iPhone or iPad - Apple Support

Regarding the Apple Books app, note that can be removed from the Home Screen without being deleted. Go to the App Library (swipe left past your last Home Screen). From there you can touch and hold an app and slide it to the Home Screen.

If it was deleted, see the following from Delete built-in Apple apps from your iPhone, iPad, or Apple Watch - Apple Support

Restore a built-in app that you deleted

1. On your iPhone, iPad, or Apple Watch, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app.
3. Tap the Redownload button .
4. Wait for the app to restore, then open it from your Home Screen.

On your iPhone home screen, swipe from right to left to very last page, where you'll find the App Library. Look for them there and using your finger, you can move them back wherever you want.

If you permanently deleted them, open the App Store App and redownload them from there.