function StringToDateTime(DateStr: String): TDateTime;
var
  FS: TFormatSettings;
begin
  FS:= TFormatSettings.Create;
  FS.DateSeparator := '-';
  FS.DateSeparator := ':';
  FS.ShortDateFormat := 'dd-mm-yyyy';
  FS.ShortTimeFormat := 'hh:nn:ss';
  try
   Result := StrToDateTime(DateStr); //the format of the string is different
   // ios : m/d/y
   // android : dd/mm/yy
  except on E: Exception do
   ShowMessage(e.ToString);
  end;

end;