It's easier just to buy a working NES Game Cartridge Holder as it's difficult to keep it work correctly after the plastic that holds the metal pin becomes worn at the pinnacle. That's generally what causes the problem of the cart "staying down," or the cart "refusing to stay down." Both are caused by a worn plastic bushing. They're relatively cheap so why hassle with trying to reposition the pin? You can buy one here:
http://nesrepairshop.com/online_shopping/index.php?productID=124