Delphi sending value between two windows - createparams overriide

Hello I have main form and two another forms. Both have this code on createparams

procedure TfrForm2.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do
  begin
    ExStyle := ExStyle or WS_EX_APPWINDOW;
  end;
end;

and both (TfrForm2 and TfrForm3) are opened from main form by using code :

with TfrForm2.Create(Application) do
  try
    Show;
  finally
  end;

So i can have 3 buttons on taskabr (main,form2,form3). But how can i send data (for example integer value) between form2 and form3 or bring to front form2 from form 3 (by clicking button etc on form 3) ? ?

Best regards Bartek