Like this:

my $set_file_name = '.1.3.6.1.4.1.429.1.2.4.5.0';
my $set_setfile = '.1.3.6.1.4.1.429.1.2.4.3.0';
my $result = $session->set_request(
   -varbindlist => [
     $set_setfile, INTEGER32, 10,
     $set_file_name, OCTET_STRING, "config.cfm",
    ]);

$result or warn "error: @{[$session->error]}\n";
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