You will probably have to remove a bunch of pretty plastic and tin parts, to find the part that the other end of the cable attaches to on the engine. If the unattached by you, end of the cable has an ell shaped end on it, it will just slip down in where the old cable was fitted. You might have to hold the spring-loaded arm or plate back to get it in there.

Just follow the old cable to where it attaches to the engine. Replacement should be about as simple as swapping the derailleur cable and sheath on a bike.