see [HowTo]: joining multi-part movies files with MKVtoolnix GUI
Second-best option is to indicate the two parts to Plex: Naming and organizing your Movie files | Plex Support
see [HowTo]: joining multi-part movies files with MKVtoolnix GUI
Second-best option is to indicate the two parts to Plex: Naming and organizing your Movie files | Plex Support