The H7 bulb plugs into the two slots on the holder.
Now I see it.
Correct me where I'm wrong. You plug the halogen H7 into the electrical socket first. Then you push the whole assembly into the headlight in such way that the two tabs (one over under your thumb) you can see in the first picture will slide into the "wider" parts of the socket in headlight. Once inside you twist it and it locks.
It is not the typical spring lock like most of the headlights have. I guess KIA makes it harder to fit HID...
It is hard to see in the 2nd picture that the socket is actually like a tower with two cuts where the tabs will fit in.
So, if this is true, and the adapter from DD does not work, I could try to find a replacement electrical socket. With this in hand, drill it inside and use it as a locking one for HID. I would avoid destruction of the original one, though.
Now, the problem I see here is correct position of the HID lamp. Your headlamp does not have any groves locking the light bulb, it happens by twisting the light bulb with the socket and locking the whole assembly in place. This cannot be done with HID as it will be "loose". Unless, the halogen locks in place by stopping on the small tab you find in H7.