How set default app preferences for KDE apps on Ubuntu?

I use kfind on Ubuntu. I need to set the default apps it uses to launch files it finds.

By default, it attempts to launch kde apps. I usually either don't have them, or don't want to use them.

I most especially want it to launch Thunar when I click 'open parent folder' on a search result.

But I cannot see where to do this. I installed 'systemsettings', the kde config app. But that seems to have no option to set default apps. I looked in ~/.kde/share/apps/ and ~/.kde/share/config, but could find no config setting. I can't see any version of kconfig or kcontrol to install.

So how do I change this setting for KDE apps in Ubuntu?

UPDATE:

In answer to Michael Clare (thank you), xdg-mime thinks my default is Thunar. And indeed it is. But not for any KDE app.

$ xdg-mime query default inode/directory
Thunar-folder-handler.desktop