Use the /g (global) to find all occurrences in a string. Place the matching statement within a while loop and count until you get to the wanted number.

$n=5;  #want the 5th occurrence of a group of 5 numbers
$count=0;
while(/(\d{5})/g){
   if(++$count==$n){
      print "The $n\th occurrence was $1\n";
   }
}
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