Most set top boxes are clearly marked with a slot saying "Viewing Card", but some set top boxes have a cover flap over the slot so that isn't immediately visible. In this instance you will need to open the flap to find the slot. After you have inserted your new viewing card, close the flap to protect it.

Please note: Your own set-top box may look slightly different to those pictured. However, the card slot will be in a similar location.