You obviously didn't understand my first point. You need to use more frames. Frames are like invisible boundaries which are packed just like any other object. You have 3 menu choices. I would make 3 frames, one for each choice. Each choice has 3 objects, a label, entry window, button. To display a frame, pack it into Mainwindow or perhaps another frame. To remove a frame from view, unpack it. I don't have time to write the code right now, but that should work. At any time, you will have zero or one of the 3 "choice frames" packed and view-able.

To clear the entry window, set the -textvariable variable to a null string.

Try the above and see what happens.

Update: I used the wrong terminology, instead of "unpack()", use "packForget()". My idea was correct, but name was wrong. Use "packForget" to remove an object from being displayed. I did a quick hack to my previously posted code, only for the "reset password" menu. See Below.

Click on Menu->password reset option, gives display of the reset objects, enter a user, hit ok on the confirmation pop-up, that will print to stdout and also clear the 3 reset objects in the window. Going through Menu->password reset option again will repeat this behavior. Note the reset to the $user variable.

Homework for the OP: Make more Frames. Probably a MenuFrame and at perhaps even a "work frame" packed into the MainWindow. You can make a frame for each of the menu options. Then pack() or packForget() those frames into either the "work frame" or the Mainwindow to show or not show them. In my hack I just directly packForget() each of the individual widgets, don't do that. Use a frame to group them together. My code is just "proof of concept", not finished code. There are hide and un-hide options for entire windows.

#!/usr/local/bin/perl
use strict;    
use warnings;
use Tk;    

 
my $mainwindow = MainWindow->new();
$mainwindow->geometry("600x150");
$mainwindow->title("Add/Delete/Reset Password");

# Disable the window Resize
# $mainwindow->resizable(0,0); # Why??? don't need it?
 
my $main_menu = $mainwindow->Menu();

$mainwindow->configure(-menu => $main_menu);

# File
my $menu_menu = $main_menu->cascade(-label=>"Menu", -underline => 0, -
+tearoff=>0);
   $menu_menu->command(-label=>"Password Reset for users", -underline=
+>0, -command=>\&Show_ResetPassword_menu);
   $menu_menu->command(-label=>"Add User", -underline=>0, -command=>\&
+Show_AddUser_menu);
   $menu_menu->command(-label=>"Delete User", -underline=>0, -command=
+>\&Show_DeleteUser_menu);
   
# About
$main_menu->command(-label=>"About", 
                    -command=>sub{$mainwindow->messageBox(-title=> "Ab
+out", -message=>"Version 3.0.0", -type => "ok")});
    
my $label_resetp;
my $entry_resetp;
my $button_resetp;

MainLoop();

my $user;  #text vasriable

sub password_reset
{
    my $answer = $mainwindow -> messageBox(
           -message=>"Password Reset for user: $user",
           -title=> "Password",
           -type=>"YesNoCancel",
           -icon=>"info");
           
    if ($answer =~ /yes/i)
    {
       # code to reset password goes here....
       
       # whatever log messasges you want
       print "PASSWORD RESET SUCEEDED: $user\n"; # a log entry?
    }
    else
    {
       print "PASSWORD RESET ABORTED: $user\n"; # a log entry?   
    }
    
    $user=''; # clear the user name entry field
    $label_resetp->packForget();
    $entry_resetp->packForget();
    $button_resetp->packForget();
}                

sub Show_ResetPassword_menu 
{

    $label_resetp = $mainwindow->Label(-text=>"Password Reset for user
+ ", -width => 40) -> pack ( -side=>'left');
    $entry_resetp = $mainwindow->Entry(-width => 30, -textvariable =>\
+$user )->pack(-side => 'left');
    $entry_resetp->bind("<Return>", \&password_reset);
    $button_resetp = $mainwindow->Button(-text=>"Click to reset", -com
+mand => \&password_reset , -width => 15) -> pack ( -side=>'bottom' );
}

sub add_user
{
    my $answer = $mainwindow -> messageBox(
               -message=>"Add user: $user",
               -title=> "Password",
               -type=>"ok",
           -icon=>"info");    

}

sub Show_AddUser_menu
{
    my $label_adduser = $mainwindow->Label(-text=>"Add user ", -width 
+=> 40) -> pack ( -side=>'left');
    my $entry_adduser = $mainwindow->Entry(-width => 30)->pack(-side =
+> 'left');
   # $entry_adduser->bind("<Return>", \$adduser_handle_return);
    my $button = $mainwindow->Button(-text=>"Click to reset", -command
+ => \&adduser, -width => 15) -> pack ( -side=>'bottom' );

}

sub Show_DeleteUser_menu {
my $deleteuser_handle_return;

my $label_deleteuser = $mainwindow->Label(-text=>"Delete User ", -widt
+h => 40) -> pack ( -side=>'left');
my $entry_deleteuser = $mainwindow->Entry(-width => 30)->pack(-side =>
+ 'left');
   $entry_deleteuser ->bind("<Return>", \$deleteuser_handle_return);
my $button = $mainwindow->Button(-text=>"Click to reset", -command => 
+\$deleteuser_handle_return, -width => 15) -> pack ( -side=>'bottom' )
+;

        $deleteuser_handle_return = sub {
        $mainwindow -> messageBox(
                -message=>"Delete User",
                -title=> "DELETE",
                -type=>"ok",
                -icon=>"info");    
                                    }

}
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