One possibility would be to use the Combined Fields capability of Tableau Desktop. Combining Region and Customer ID to one field.
To create a combined field:
1. CTRL + Select: [Region] + [Customer ID]
2. Create > Combined Field
3. Drag newly created combined field to columns shelf.
I have created a small sample workbook that I am attaching as well.
Source: Combine Fields
Additionally, if you could attach a packaged workbook that you have been working on there is a better chance that someone in the community can assist.
I hope this helps!
Combined Field Example.twbx 387.6 KB