It requer you to mod the game with BepInEx to use plugins.
here is The last BepInEx stable ver download link -
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It also need the game engine to have some unstripped dlls to work, you can get them by creating clear unity project in Unity Hub using same engine version as the game. But since i already done that, you can get those from me and simply follow this guide.
1 Unzip BepInEx into your KK folder
2 Unzip Dllstouse with file replace into same KK folder
3 Start and close the game once (if a plugin folder appeared in \KoboldKare\BepInEx you did all right)
4 Now you may add plugins into that plugin folder and its done