If the script is a single .js file you can follow Toon Boom’s instructions:
If there is a .ui file put it in the same folder as the .js file.
If there are icons just put them in the default ‘script-icons’ folder.
The scripts that have an .ui file may need to be edited depending on the Harmony version you are using.
In the .js file look for the lines that contain something like this:
Then replace with the right folder name, if you are using Harmony 11.1 it would look like this: