You try something like this ...

#!/usr/bin/perl -w

use strict;

use Tk;
use Tk qw(exit);
use Tk::DialogBox;


my $FILE1 = "Please select a file";
my $FILE2 = "Please select a file";

my $top = MainWindow->new();

my $thebutton = $top->Button( 
    -relief => "groove", 
    -text => "Click Me ", 
    -command => \&thebuttonCallback)->pack();

sub selectFile1Callback  {
    my $userSelectedFile = $top->getOpenFile(
        -defaultextension => ".ctl",
        -filetypes    => 
            [
                ['Control Files', '.ctl'],
                ['All Files', '*']
            ],
        -initialdir    =>    "C:\\TEMP",
        -initialfile    =>    "Junk.txt",
        -title        =>     "Select file 1"
    );
    if ($userSelectedFile) {
        $FILE1 = $userSelectedFile;
    }
}

sub selectFile2Callback  {
    my $userSelectedFile = $top->getOpenFile(
        -defaultextension => ".ctl",
        -filetypes    => 
            [
                ['Control Files', '.ctl'],
                ['All Files', '*']
            ],
        -initialdir    =>    "C:\\TEMP",
        -initialfile    =>    "Junk.txt",
        -title        =>     "Select file 2"
    );
    if ($userSelectedFile) {
        $FILE2 = $userSelectedFile;
    }
}
[download]

There is a lot of room for improvement.
You only need one selectFileCalback.
Hope that helps

--
Its like a dog that can sing and dance.
It's remarkable because it can do it.
Not that it can do it well.