Before doing any of these steps, make sure your game is closed.

1) download this:
https://github (dot) com/BepInEx/BepInEx/releases/download/v5.4.22/BepInEx_x64_5.4.22.0 (dot) zip

2) go to your steam library, right-click Lethal Company, click "properties", then click "Installed Files" -> "Browse". This will open a window with your game's files.

3) extract all the contents of BepInEx_x64_5.4.22.0.zip file into a folder in your Lethal Company files. So, in your Lethal Company folder, you'll just have the game files, a folder "BepInEx", and 3 other files from the .zip you downloaded.

4) If you've done the first 3 steps correctly, the BepInEx folder should have only 1 thing inside: a folder called core. Now, start up your game, get to the title screen, and then close it. After doing this, several new folders should appear in the "BepInEx" folder alongside "core". One of these folders is "plugin".

5) Go to this page and click "Manual Download":
https://thunderstore (dot) io/c/lethal-company/p/notnotnotswipez/MoreCompany/

6) Extract the zip, then inside you'll see another BepInEx folder with its own "plugins" folder. In there, you'll find "MoreCompany.dll". You'll want to move this file into the new "plugins" folder that was created inside your game's files (Lethal Company\BepInEx\plugins).

7) Now start the game again, and you should see the title screen has changed to say "More Company". This means the mod has installed successfully and you can join other players using the mod!