my %User_Server = MapUsersToServer();

my $Rows = $worksheet->SomeMethodICan'tRemember();
foreach my $row (@$Rows)
{
    my ($user_id, $server) = ($row->[5], $row->[6]);
    if ($User_Server{$user_id} ne $server)
    {
        # Do something useful here.
    }
}