Try what jaldhar suggested, but if you want to learn how to use thread, check out the attached code, which is a multi-thread version of your code.

use strict;
use warning;
      
use Net::DNS;
use threads;

sub resolve {
    my $res = Net::DNS::Resolver>new; 
    $res->nameservers();      
    my ($nameserver, $url) = @_;
    my $query = $res->search($url);                        
    $res->print;
    my $result;
    if ($query) { 
        foreach my $rr ($query>answer)  
           next unless $rr->type eq "A";
           $result = $rr->address;
        }
    }    
    return [$url, $result];
}

my $nameserver = "12.104.122.2";
my @url = ("www.perlmonks.com", "www.foxnews.com");
my @thread_pool;
foreach my $url @url {
    push @thread_pool, threads->new(\&resolve, $nameserver, $url);
}
my @result;
foreach my $thread @thread_pool {
    push @result, $thread->join;
}
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