Breakdown England map to region

I dont have much experience in building map in Tableau and I hope someone could help me.

I have a map which contains EU5 countries. In this map, I manage to group them into the regions I want for all countries except UK. For UK, Tableau cannot breakdown England map into the regions as below. The screenshot would be the display i want to achieve. I have also attached the twbx file I have build. Any idea on how to build this?

East England

East Midlands

London

North East/ Yorkshire and Humber

Northwest England

South East England

South West England

West Midlands