You can reinstall the Nokia Music from the Store application in your device. If you can't find the Nokia Music application in the store, you can select any other application visible and tap on the more from Nokia Corporation option. By doing this the Nokia Music should appear also. If you still can't find it, make sure that you have properly set up the Region and Language settings in your phone.
To be noticed that the Nokia Music application is only available in some countries. For more information you can check the following forum.