1. Once the data is loaded, open the App overview window and create a new sheet.
2. Enter the Edit sheet mode on the sheet.
3. Create a Table object.
4. Add Country as the dimension.
5. Next, add the following measure and label it No of Customers:

Sum([No of Customers]) 

6. Under Appearance, open General and, in Title, add the following expression:

=Max(aggr(Sum([No of Customers]), Country)) 

7. Next, in Subtitle, add the following expression:

=Firstsortedvalue(Country, -aggr(Sum([No of Customers]), Country)) 

The resulting table will look like this: