Ah - so you have already separated the two. You might just be able to show us the relevant part of your CGI program which produces the output, but I presume your program currently still looks like the following:

#!perl -w
use strict;
use CGI;

do_all_the_initialisations;

while (1) {
    my $information = get_information;
    print <<HTML;
This is my HTML page with $information
};
[download]

And basically, that's not how CGI works. A CGI program is supposed to output one page worth of HTML and then exit. So you will either need to get rid of the loop and (re)do the initialization, or create the HTML page from a third program every 10 seconds and just serve that page as a static HTML file.