Mallet assembly help!

I’m a bit confused about how to put together the mallet attachment!

I got up to the step where there’s a chisel… but then no info about what to do with the chisel. In the following pictures it looks like the shaft of the plastic part is missing entirely, so am I to remove the shaft? If I do that, it seems like the thing wouldn’t work at all!

Thanks for any guidance!

I have the same question as I can’t assemble without the shaft of the plastic part.