Ours is a Ford Lehman, but I’m not sure that it’s the same marinisation as yours: ours has a large engine-cooling-water heat exchanger on the RIGHT side of the engine as you look from the stern (and it’s painted red).
If yours looks the same, then near the FRONT, but on the TOP of the heat exchanger cylinder, there’s a largish nut ..from memory it’s a bit larger than half an inch.
Unscrew that nut on the TOP of the exchanger, and it should pull up and dangling beneath it should be the remnant of the previous cylindrical zinc anode ..or the previous anode may have dissolved away, or dropped off into the heat exchanger chamber. (Old detritus of previous anodes can be removed by unscrewing the very FRONT of the exchanger, and clearing out the crud.)
Then insert a new cylindrical zinc anode into the bottom of the nut, and screw back into the exchanger.
If none of this seems sensible, then perhaps your marinisation is different from ours, even though it’s the same engine.
P.S: If the picture which I’ve just uploaded is visible, or reachable, it’s of our heat exchanger (you don’t have to remove yours, but we did, for maintenance) and the nut at the very top-right of the picture is the nut which holds the anode: just unscrew it to remove the previous one and to replace it with a new one.