Apple has created a dedicated page related to music restoration from iTunes. You can check it below. However, if your files were deleted, then you need to check the Recycle Bin or Trash (Mac). Locate the files and right click or click them and choose Restore. Restart iTunes and the files will be available for playback. The files in iTunes that are not in their original location will be marked with a yellow exclamation sign.
Support page: https://support.apple.com/en-us/HT203167
