A far as I understand you are looking for a way to join these two CSV tables on 'CI Name' = 'DeviceName' .
You can apply the answer of PowerShell: Combine two tables.
The only you have to do is to change the way you import one of the CSV file :
Import-Csv 'Csv1.csv' -Header "DeviceName", "region" "xyz", "London abc", "Cairo lmn", "Brisbane qrs", "Sao Paulo"
Perhaps you have to remove the previous heaser first.