The reverse directive is just a “Reverse Index”. You don’t need to add anything. It is automatically added based on the parent.
For example. If you add a user Bob. And later you wanna add a post from Bob. You should add "uid": "uid_from_Bob, "posts": [{MY NEW POST}]. The direction is always Parent to => Child. So, the creation of the post must come with Bob’s UID and the edge posts.
To retrieve Bob when query the post you just need to use the tilde notation in the query block request.