From the home screen select settings and then Home, devices. Select the device you want to reassign and select the name showing under Room. Adjust room name and relocate device accordingly.
If this doesn't work, phone technical support.
I have exactly the same issue. Can’t complete 2 radiator valve installations on Tado app because of it. Strangely the rads do show up in Apple HomeKit and can be controlled from there. Also awaiting call back from support but if you hear first......
Thanks for your response. Hope you get this sorted.
Support came back to me to say that I could now create and assign rooms. I was able to do this and complete the installation.
They didn't tell me what was wrong, but it all seems to work now. I do have two further valves to add- hope they work!
There is an issue that, under certain circumstances, the system can't reconfigure the devices correctly (e.g. which rad-stat is allowed to call for heat from a specific Smart Thermostat). This can lead to you being road-blocked and support having to resolve it for you.
We are working on fixing this, but it may take some time to get it to automatically be able to account for any configuration change.
I apologise for the inconvenience this can cause.