If your door frame has a hole for the handle extension of the door catch mechanism and has the extension then put some plasticine in the hole and offer up the mechanism again. This will leave an indentation in the plasticine and will give you a guide as to where to drill the door skin. It won't necessarily be central to the frame hole. If your frame does not have a hole for the handle (and thus no extension on the lock mechanism but a square hole for an insert) then put a thin film of plasticine on the frame and offer up the mechanism. This will leave an impression in the plasticine to use as a guide for drilling the frame. I've no experience of the latter as mine already has a hole in the frame to accommodate an existing extension.
