configure xdg-open to handle protocol

Hi all,

I’m trying to download assets from the unity asset store, but xdg-open don’t seem to know what to do with it.
I have unity on my system. When I open the link in my browser (chrome) it says it will use xdg-open to handle the link. But then I get an error: Unable to run the command specified. The file or folder file:///home/user/com.unity3d.kharma:content/13866 does not exist.

I found out that i need to edit xdg-open to associate the protocol com.unity3d.kharma with Unity 3D.
But how and where do i do that?

Thanks for your reply in advance!