@ENTHU,
A couple items, you are looping thru 4000 rows twice. You might want to loop once. You can use For Each Row( stmt1; stmt2 ) or a for loop. Also your code has dt:col2 = Substr( Char(dt:col2), 3, 2). Why do you have the Char() function? Does col2 have Character data type?
Below is an example using a For Loop, assuming col2 is defined as Character data type. You should look at the values in row 161
For(i=1, i<=nrow(dt), i++,
dt:col1[i] = word(1, dt:col[1], "S");
dt:col2[i] = Substr( dt:col2[i], 3,2 );
);