Welcome to the Apple Support Communities!
I understand that you need to enable iCloud Music Library but you aren't able to find the option in the settings on your device with iOS 11. While the settings have not changed for iCloud Music Library in iOS 11, I will be glad to guide you to resolve this question.
You will find the feature by going to Settings > Music > Show App Music (needs to be enabled) > iCloud Music Library (needs to be enabled)
Turn on iCloud Music Library
You can always try to update your device to the latest iOS version 11.1.1 by going to Settings > General > Software Update. If there's an update, tap Download and Install. If your iOS is already up to date, you see the latest version number and no option to install a new version.
Hope this information is helpful. Let me know if you need additional help.