Installation
The file you receive is a single .unitypackage. Importing it into the project is the whole installation.
Import
- Open the avatar project in Unity. Use Unity 2022.3 LTS.
- Choose Assets > Import Package > Custom Package and select the
.unitypackage. Dragging the file into the Project window does the same thing. - Click Import in the import dialog.
The file is named me.kamyu.tooncolorassistant-<version>.unitypackage. After import it lives at Packages/me.kamyu.tooncolorassistant.
Check that it installed
The install worked when Tools > Toon Color Assistant appears in the top menu.

What you do not need to install with it
There is no extra DLL and no NuGet package. lilToon and Poiyomi are optional. The tool runs without them, and writes their properties only when they are in the project.
Remove it
Delete the Packages/me.kamyu.tooncolorassistant folder.
Colours and numbers already written to materials stay after the folder is gone. If you still want those values back, use Ctrl+Z or the window's Revert before you delete the package.