Not sure what you want:
There are lots of ways to sort this stuff once we agree on the data to be output. Since $rHol is a reference, you need the -> operator to deference the key, normal hash would be just $Hol{$key}, but you need $rHoL->{$key}. Then you need {} around that whole thing to tell the @ operator what to operate upon.

#!/usr/bin/perl -w
use strict;

my $hash_ref= {1002=>[1,2,3,4,5],
               1001=>[6,7,8,9,10],
               3   =>[2]};
               
print_HoL($hash_ref);

sub print_HoL
{
   my $rHoL = shift;
   foreach my $key (keys %$rHoL) 
   {
      print "$key: @{$rHoL->{$key}}\n"; 
   }
}
__END__
Prints:
1001: 6 7 8 9 10
1002: 1 2 3 4 5
3: 2
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