It looks to me like you want to keep a running total. If so, do something like this

my $total=0; # running total
foreach (@temp) {
    my ($instan, $value) = (split /\*/, $_);
    my $k = $key . ":" . $instan;
    $total += $value; # total for each iteration
    $DM_D{$k} = $total;
}
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poj