If you follow the process here, most of your media should be associated with the existing data. You will know that it worked properly if, after copying the media, adding the new location to your library, and scanning, your episodes show up with duplicates. Just be careful to follow the steps precisely, particularly the step of copying the media to the new location, not moving it.
If any shows don’t show up as duplicates (due to matching errors) you can match/fix match on and then merge with the existing show. After you’re satisfied that everything has been detected properly and is using the existing metadata, you can remove the original media directory(ies) from your library.
If you still have issues, you may want to check out this thread. However, it requires manual database modification:
