This is the picture of your crank?


https://www.bikeforums.net/g/album/30840372


I think it's a self extracting crank. You need to leave that cap on and then put a 10 mm hex key in it and turn it counter clockwise. The instructions are basically printed on it right there. Though they are talking about putting it on. And yes it might be sort'a hard if you have a short hex key. They sell longer ones.

Welcome to BF. If you need to post any more pic's before you get 10 posts, then just let us know in your post that you put them in the Gallery.