add plugin to plex on synology nas

[Hotboy1987]

I have synology nas ds720+ and I add plex media server to it to play my local movies and series ,, and I use arabic subtitle some of it show strange characters ,, after some search I found that this plugin can solves my problem ,, I download it and but it in this folder

/volume1/PlexMediaServer/AppData/Plex Media Server/Plug-ins/SRT2UTF-8.bundle

but when I go to my plex media server to the Plugins it show No plugins installed.

some help here