Basically there is no way to fully delete steemit posts but there is a way that you can "hide" it or let's say "delete" it
So let's say that you've copied a post from a blog and you've submitted as a story that you've created on steemit, and then you got this message
So now you want to delete your post
What you do is go to your post and press "edit"
And just put the name to empty or whatever you like and put the description or story to i just want to delete this post
it was a spam or something like that
As i said you can not DELETE a post but you can basically hide it or at least it wont be the same