Have you simply tried prioratising them to do one? Crafting encompases many, many diferent activities, so they might jsut be doing something else in the mean time. Just try to force one to craft it.

i tried that 2 times but don,t work maybe my game is bugged

Not sure if you've already worked this out, but it seems to be a bug that you can add the bill to the fishing dock.

You can add the bill and make the harpoon at the fueled and electric smithy production tables, same as other melee weapons.

Maybe it's aa smithing job instead of a crafting job?

i could never get the harpoon to get made and this is with all jobs on 3 then me manually assigning someone to craft but all they do when you manually assign them is fish.

Harpoon and fishing rod have been removed since A16.