FreeNAS
go to Plugins - select PlexMediaServer
[Install]

Go to the Plugin - select Installed
change Service Status to ON

Go to Jails
there is a plexmediaserver_1
if you select [Edit] you could change DHCP to FIX IP

in Storage

Source you select the Share with your Videos
Destination you select
/var/db/plexdata/Plex Media Server