[RobinB]

I contacted KIA UK, which refused to send a PDF owner's manual, but confirmed that voice commands cannot change the temperature or control the vents.

Have you tried downloading the "Kia Owner's Manual App (Official)" from Kia Corp. on the Google Play Store (or Apple equivalent)?
See the discussion "Kia Owner’s Manuals - there’s an app for that!"
It doesn't give you a PDF which you can open on a PC, but at least you can browse the manual from an app and search it like you might a PDF and follow links from the contents list etc.