You might be struggling to find a third-party remote which has a button to change the screen format, you may well have to buy a replacement from the TV manufacturer.
But one thing's for sure, you can't change the screen format using the TV buttons.
unless the tv has buttons on it for controlling the settings menu (assuming it has a settings menu that has options for changing the screen type) you need a remote. go to walmart or something and pick up a universal but make sure that it has a button on it for changing the screen type from normal to wide to zoom etc.
You might be struggling to find a third-party remote which has a button to change the screen format, you may well have to buy a replacement from the TV manufacturer.
But one thing's for sure, you can't change the screen format using the TV buttons.