Okay I looked into it because I didn’t quite understand what you were talking about.
What One-Click Child Theme allows you to do is make a child of a theme (in this case Spacious). The “design directory” you are talking about is probably the “Theme Options” which is a property of the parent theme. It should be there. (I installed Spacious and child theme’d it successfully in the 1.5 version of the plugin.)
However in the older version of One-Click Child Theme, I didn’t create a functions.php file because the behavior of WordPress themes was different when I wrote it 4 years ago. It could be you couldn’t access the Theme Option because of this missing file. If this is the case, update to the latest plugin and go to Appearance > One-Click Child Theme and click on the Repair Child Theme button (if it’s not there, it thinks everything is good). It should upgrade the child theme according to the modern rules and the Theme Options should work correctly.
If, on the other hand, you want to change the Theme Options by hand, that would involve overriding functions in functions.php which is not an easy thing.
I hope this helps.
