Plex has a hard time reading VOB files, so you'll be better off using MakeMKV to remix them as MKV files. You won't lose any quality, but you will lose access to menus. Chapters will be preserved. Visit makemkv.com/ and click the "Download Make MKV for Windows" link to download the installer. You can leave all of the installation settings at their defaults. MakeMKV will not install any adware. You can start it from the installation wizard, or from the shortcut on your desktop. You'll find this in the upper-left corner of the MakeMKV window. It looks like an icon of a camcorder over a file. If you ripped the VOB files from a DVD, they'll typically be located in a VIDEO_TS folder. Navigate to this folder in the file browser so that you can see the contents. This is the master file for the VOB files, and tells the player which order to play them in. Selecting this file will allow MakeMKV to load all of the VOB files into the MKV file. For movies, this should be the full-length title. If the DVD had several TV episodes, you'll have to create a separate MKV for each episode, which actually makes selecting episodes easier in Plex. You can also select the audio and subtitle tracks you want to include. MKV supports multiple tracks of each. MakeMKV will create an MKV file based on the title and audio settings you selected. The time this takes will vary depending on the size of the VOB files. Plex can read and transcode MKV on the fly, so it should have no problem picking up your new MKV file. In most cases, Plex will automatically find the correct information for the video. See Set Up a Media Server Using Plex for details on adding media to your Plex server.

TL;DR in Vietnamese:
Tải MakeMKV. Khởi động trình cài đặt và làm theo hướng dẫn. Khởi động MakeMKV. Nhấp chuột vào nút "Open files" (Mở tập tin). Truy cập thư mục chứa tập tin VOB. Chọn tập tin "VIDEO_TS.ifo". Chọn tựa muốn xem. Bắt đầu quá trình hòa trộn. Thêm MKV đã hoàn thành vào thư viện Plex.