This solution is similar to tim's but doesn't use a second intermediate data structure. It uses the flattened hash (from the first step) inline.

# selected stores
my @st= ('STORE2','STORE3','STORE5');

# list of stores (doesn't keep duplicates)
my %stores= map { %$_ } values %bighash;
                                                                      
+          
foreach my $store ( sort { $stores{$b}[0] <=> $stores{$a}[0] } @st ) {
  my $products= $stores{$store};
  my $earned  = shift @$products;
                                                                      
+          
  print "STORE: $store EARNING: $earned\n";
  foreach my $product ( @$products ) {
    print join( "," => @$product ), "\n";
  }

  print "\n";
}
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As tim says, without a more detailed problem description, it seems that the extra level of nesting in %bighash (set1, set2, etc.) is unnecessary.