my $n = 2;
my $pattern = qr/\.0/;
my $string = "This is the .0 test .0 string .0";
$string = delete_nth( $string, $pattern, $n );
print $string, "\n";

sub delete_nth {
    my ( $str, $pat, $n ) = @_;
    $n--;
    $str =~ s/($pat.*?){$n}($pat)/$1/;
    return $str;
}