august3,
Your wording leaves a fair amount to be desired. I can see at least two interpretations:

• Given a value, list all corresponding keys
• Produce a list of values that have multiple keys

The first one is easy:

my @keys = grep { $hash{$_} eq 'value' }keys %hash;
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The second is just a bit more work:

my %value;
push @{ $value{ $hash{$_} } }, $_ for keys %hash;
for ( keys %value ) {
    if ( @{ $value{$_} } > 1 ) {
        print "$_ :\n";
        print "\t$_\n" for @{ $value{$_} };
    }
}
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