my $cause='"Id"=?'; # oder was du da stehen hast
my $sql = qq(update "CUST" set "$field"=?, "Date"=?, "Time"=? where $cause);
my $sth = $dbh->prepare($sql);
for my $datensatz (@datensaetze)
{
  my ($to,$dat,$time,$id)=@$datensatz;
  $sth->execute($to,$dat,$time,$id);
}

$sth->finish();