If you have not done so already, you can download TouchCopy from here:Download TouchCopy Now
First, please connect your external drive and open TouchCopy options. In the save location field, select a location on your external hard drive. Close TouchCopy options and proceed copying music to your external drive as given in our online TouchCopy user guide.
You can then import your music from your external drive into iTunes by selecting the File tab in iTunes and then Add folder to library.
You can also copy your files to iCloud Drive. Saving to the iCloud Drive means all of these files will be accessible by your iPhone, iPad, iPod touch, Mac or PC, as long as the iCloud Drive App is active on each device.