# This:
foreach my $top_item ( keys %Myhash ){
    if ($top_item eq $My_Value)    {
        # do stuff
    }
}

# can be reduced to this:
if ( exists $Myhash{$My_Value} ) {
    # do stuff
}

# And this:
foreach $iteminitem1 (sort(keys %{$Myhash{$item}{$iteminitem}})){
                if(
                    $iteminitem1 eq 'name' 
                        &&
                    $user_number == $Myhash{$item}{$iteminitem}{$iteminitem1}
                ) {
                    my $User = $iteminitem; 
                }
            }

# can be reduced to this:
        if (
            exists $Myhash{$My_Value}{$iteminitem}{'name'}
                and
            $user_number == $Myhash{$My_Value}{$iteminitem}{'name'}
        ) {
            my $User = $iteminitem;
        }

# The combined restructuring yields:
if ( exists $Myhash{$My_Value} ) {

    foreach $iteminitem (sort(keys %{$Myhash{$item}})){

        if (
            exists $Myhash{$My_Value}{$iteminitem}{'name'}
                and
            $user_number == $Myhash{$My_Value}{$iteminitem}{'name'}
        ) {
            my $User = $iteminitem;
        }
    }

}