$hauptfenster->update;

...

my $ref_old = &start_frag_nach($dbh, "1");
...
my $frame_top_menu = $hauptfenster->Frame(
                                  -borderwidth => "2")
                                  ->grid(-sticky => "nw");
$frame_top_menu->BrowseEntry(-label => "Verwalten von:", 
                             -variable => \$ref_gruppe->[0], 
                             -choices => \@{$ref_gruppe},  
                             -colorstate => 'white', 
                             -browsecmd=> sub{$ref_old = &start_frag_nach($dbh, "2");$hauptfenster->update;print "$ref_old->{nachname}";})
                             ->grid(
...
sub start_frag_nach{
    my ($dbh, $id) = @_;
    my ($ref_old );
    $ref_old = &frag_nach($dbh, "select * from kontakte where ID = ?", $id, "fetchrow_hashref()",);
    return (\%{$ref_old});
}
sub frag_nach{
    my ($dbh, $sql, $id, $befehl, $eintrag, $typ_in_wert, $typ, $tabellen_name, $spalten_name, $index_name,  ) = @_;
    my ($sth, $ref, );
    $sth = $dbh->prepare( "$sql" );
    $sth->execute ($id);
    $ref = $sth->fetchrow_hashref();
    $sth->finish ();
    if (defined ($eintrag)){
        eintrag_hinzu(\%{$ref});
    }
    if (defined ($typ_in_wert)){
        #$ref_adresse = typ_in_wert_wandeln(\%{$ref}, "adresstyp_id", "adresstyp", $dbh, "beschreibung", "id");
    }
    return (\%{$ref});
}