use strict;
use warnings;

while (<DATA>) {    # go through data line by line
    chomp;          # don't forget to remove newline character
    my @fields = split /\t+/;
    print join "\t",           # join fields with tab
          @fields[ 0, 2, 1 ],  # select fields using array slice
          "\n";
}

__DATA__
Col1    Col2    Col3
a       b       c
1       2       3