[Closed] crank removal help

Hello people, im new to the forum so I will take this time to say hello and hope to have a buzz and some quality rides with some.

Right, I'm trying to replace my crank (Shimano acera octalink), i have the tools for the job and have purchased a BBB powerpull puller. There's a mushroom looking cap which can be removed apparently for octalink and Isis and left on for square tapers. I have removed the crank bolts but from what i can see there is nothing for the "pusher" to push on, as in the "pusher" is too think without the mushroom to contact anything it just fits through the hollow gap through the bb.

What's the dig? I don't want to just try it with the mushroom I case i mash it up. I'm sure you can tell i have never tried this job before and im sure im on a mad one and missing the obvious.

Thanks for any help in advance, cheers.