Cannot find library since changing modem/router

Plex Media Server
1

Server Version#:
Player Version#:
I recently got a new modem which my hard drive with my library attaches to. I can no longer access the files or see the DLNA server. can anyone help me please? I have a Cloudmesh Gateway modem with a WD hard drive plugged into the USB port which has my library files on it. I can still see my library but when I click on a movie to watch it I get this error: Playback Error

Please check that the file exists and the necessary drive is mounted.

2

With PMS installed on your Mac (according to the tags on your post) – is the drive attached to your router still shared within your home network and mounted on the Mac?
Can you confirm the path in /Volumes/... still matches with the folder name originally linked to your library?

macOS might add an index to the folder name if it recognizes it as a different drive / host.