It may help us more if you show what you've tried.

Having said that, I'll give you a very simple example that may do more-or-less what you need. It starts a worker thread which calculates the localtime every minute, and passes that to the main thread through the shared variable $ltime. It's important to keep the Tk code separate from the thread code (because Tk is not thread-safe), which is why the textvariable '$lbl_label' was kept separate from $ltime, and only assigned from $ltime from within the Tk idle loop update_gui().

You can, of course, change sleep 60; to a smaller interval to see it update more often:

#!/usr/bin/perl -w


# Libraries
use warnings;
use strict; 
use threads;
use threads::shared;
use Tk;
use Tk::Font;


# Shared variables
my $ltime : shared = 0;


# Globals
my $lbl_label = "Started";


# Main Program
my $thread = threads->create(\&worker_thread);
$thread->detach;

create_gui();


# Subroutines
sub worker_thread {
    while (1) {
        $ltime = localtime(time());
        print "Debug> In worker_thread():  Updated localtime to '$ltim
+e'\n";
        sleep 60;
    }
}

sub create_gui {
    my $mw  = new MainWindow(-title => 'Thread example');
    my $fr  = $mw->Frame->pack(-expand => 1, -fill => 'both');
    my $fnt = $mw->Font(-family => 'arial', -size => '12');
    my $lbl = $fr->Label(-textvar => \$lbl_label, -background => '#ffe
+fb5');
    my $btn = $fr->Button(-text => 'Exit (ESC)', -background => 'cyan'
+);
    $btn->configure(-command => sub { exit }, -font => $fnt);
    $lbl->configure(-font => $fnt);
    $lbl->pack(-side => 'left');
    $btn->pack(-side => 'right');
    $mw->bind("<Escape>" => sub { $btn->invoke });
    $mw->repeat(1000 => \&update_gui);
    MainLoop;
}

sub update_gui {
    printf "Debug> In update_gui():  %s\n", time();
    $lbl_label = $ltime;
}
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