if you unpack the osp addon, there should be a folder with 5 things in it.
two folders ("resource" and "textures"), two text files (.txt) and one file called "module.ini".
now copy all this into your custom settlements folder. if you do it right, it should ask you if you "really want to overwrite" some things, just press "yes all". and that's it.
if it's still not working, give a more detailed info on what exactly is happening.