I think that option is available only on desktop, and it could be under edit - advanced. If you have any problems just report your own post and explain the reason you want it deleted and a moderator will do that for you.
I'm in here on my phone via browser, no app involvement. When I want to edit a post, it comes up with edit option, but the only action I get is deleting the post. If I only want to change something, too bad, I have to retype the whole thing...