You gave the answer already (except the quotes are not needed).

my $pcname;
foreach my $objItem (in $colItems) {
   next unless $objItem->{Description} eq "...";
   $pcname = $objItem->{DNSHostName};
   last;
}
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One catch. What happens if there 0 or 2+ matching records? You could store them in an array.

my @pcnames;
foreach my $objItem (in $colItems) {
   next unless $objItem->{Description} eq "...";
   push(@pcnames, $objItem->{DNSHostName});
}
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By the way, the first snippet can also be written as

use List::Util qw( first );

my $pcname = map { $_->{DNSHostName} }
             first { $_->{Description} eq "..." }
             in $colItems;
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The second snippet can also be written as

my @pcnames = map { $_->{DNSHostName} }
              grep { $_->{Description} eq "..." }
              in $colItems;
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If you're expecting one, and only one match, you could easily check the number of entries in @pcnames.

my @pcnames = map { $_->{DNSHostName} }
              grep { $_->{Description} eq "..." }
              in $colItems;

die("Unable to find network card\n");
   if @pcnames == 0;

warn("Found multiple network cards. Using the first one\n")
   if @pcnames != 1;

my $pcname = $pcnames[0];
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