How would I go about changing to the uk version, I side loaded mine will I have to switch back to the previous version to get the one ui official update??
So I can't categorically say as I haven't received an OTA update yet. You can downgrade using Odin (I haven't used this before) and then sign up again or do what I did and sideload the latest 2 versions (you have to do them in order), see link below. https://forum.xda-developers.com/galaxy-s9-plus/how-to/galaxy-s9-s9-one-ui-android-pie-beta-t3867446...
Will repeat still yet to receive OTA update though, but that might be because there isn't a newer version
ZRKA was just the initial beta software that wasn't released to the UK, ZRKN is just an update to that. If you search around in that XDA link you should be able to get the updates and sideload via sd card or adb