With the release of iTunes 12.7, Apple removed the built-in App Store; however, it has released iTunes 12.6.3 for those who still require the functionality.
Apple offers Volume Purchase Programs and Apple Configurator on Mac to help enterprise environments manage and mass-deploy apps on iOS devices. But certain business partners might still need to use iTunes to install apps. If you've already installed a newer version of iTunes, you can download this version of iTunes on your Mac, PC 32-bit or PC 64-bit and run the installer. After installation is complete, you can continue to deploy apps with iTunes.
You won’t be prompted to download new versions of iTunes after you install this version.