Hi Teddy, there are instructions for installing a script here:
https://moi3d.com/faq#Q:_How_do_I_install_a_plug-in_script.3F

It sounds like you've done that ok, you want to place it in
~/Library/Application Support/Moi/commands

After it is installed there won't be any immediate visual change in the UI, you need to set up a shortcut key to trigger it. More details at
https://moi3d.com/faq#Q:_How_do_I_install_a_plug-in_script.3F

Can you post a .3dm file with problematic curve? Or if you want to keep it private you can e-mail it to me at moi@moi3d.com

- Michael