I haven’t played any of the Monkey Island games yet.
When I first entered the forest I tried a few paths at random before I happened to notice that the Navigator’s Head was spinning in my inventory, so I thought “of course I should use the Navigator’s Head to navigate, duh”.
Exiting and entering the forest again, I followed the Head’s pointers and found this secret site thing. I left the forest and tried the same method again from the beginning, and this time ended up at the Thimbleberry bush. I can’t tell you what path I took each time. I figured that the Head must lead to the bush but I made a wrong turning on the first attempt.
I have resumed the game with no problems. It’s good to know I don’t have to restart.