The lid is opened and closed via a push-up pin, which can be adjusted by turning it in a clockwise or anti-clockwise direction.
If you are unable to close the lid properly, this is because the push-up pin is too high. Turn the pin in a clockwise direction until the lid can be closed.
If you are unable to open the lid, place the Premier on a firm surface. Carefully turn the cooler upside down and shake it gently until the lid releases. Then place the cooler back on its feet and turn the push-up pin in an anti-clockwise direction, so that it sticks out a little higher and the lid can be opened easily.