I was looking at an app from the US app store, now I can't find out how to change store back to UK? When trying to update apps I had previously installed I get the message "Account not in this store", saying I must leave the US store. 

My region is UK and I have Apple iD and valid payment for UK. 

How do I change back to the UK store? 

I even tried creating a new Apple iD and still have the same issue.
If you are on iOS 12:

Go to the AppStore. At the bottom tap on today.

Then tap the avatar in the top-right as show below:



Then click on your name/email at the top. 

Then you should be able to change your AppStore/check your country or region there: