drag drop your country field on report
open property by right click that field ->
Format Object
on that page at below you will see
display string and a button
x+2
click that button and put below formula in editor
YourCountryField=> select it from
Report Fields -> your contryname field
e.g.
{Table.CountryNm}
MID(YourCountryField, 1,3)
Happy Coding!
:)