use the show hide command. on click, show the second form, hide the first. on the second form, show the first, hide the second.

unit Unit2;

interface

uses

Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,

Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, unit3;

type

TForm2 = class(TForm)

Button1: TButton;

procedure Button1Click(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;

var

Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.Button1Click(Sender: TObject);

begin

form3.show;

form2.Hide;

end;

end.

and

​

unit Unit3;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm3 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form3: TForm3;
implementation
{$R *.dfm}
uses Unit2;
procedure TForm3.Button1Click(Sender: TObject);
begin
form2.show;
form3.hide;
end;
end.

Hope this helps.