The hole in the top of the can is to release the hot gases created when charring the cloth inside. If the lid doesn't fit too tightly, you may be able to get away without it, but it may also let too much oxygen in, and all you will have left is a pile of ash. On a tight fitting lid, without a small hole, those gasses will pop the lid off, allowing too much oxygen to flow in, and all you will have left is a pile of ash.

Poke a hole in the can with a small nail, then plug the hole with the nail as soon as you pull the can off the fire, and allow it to cool before you open the lid.

you should but then put a rock or something flat to let only a tiny bit of air out.