It seems that the criticism about the disappearance of the iTunes App Store with the arrival of iTunes 12.7 has been heard and Apple has decided to give the option to continue accessing the app store from Mac and Windows .
Apple has chosen to release a new version of iTunes that offers this possibility, 12.6.3. However, branch 12.7 of the software remains unchanged and will not incorporate access to the App Store again, at least for the time being.
If you miss being able to access the App Store and install ringtones from iTunes, all you have to do is download the 12.6.3 installer for Mac or PC (32-bit or 64-bit) and install it on your computer.
The installer will automatically remove version 12.7 and install version 12.6.3 with access to the App Store and ring tone installation without losing any data.
This new version of iTunes is compatible with all Apple devices (including iPhone X and iPhone 8) and of course also with the new iOS 11 . In addition, Apple has ensured that those who install this version of the software will not be notified of new versions of the 12.7 branch of the program.
In TodoAppleBlog : How to create custom ringtones on iPhone