Item stuck in rear vent of a Leisure range cooker CMTG94?

When opening a bottle on the benchtop next to the cooker, the metal bottletop accidentally dropped into one of the slots of the vents at the rear of the hob. Any ideas about how to get it out without an expensive visit by an engineer? Both gas ovens give off a smell of fumes since the top slid into the vent, so it must be blocking part of the vent and so I need to get it out.