If I am not mistaken there are twqo spots where you can wall jump on FD.
One is the ledge wall.
The other is further down, where you see pieces circling the whole stage.
To ensure getting a wall jump on the second part try this:
Hang on to the ledge.
Then let go by tapping away. emediatly hold towards the stage. You should fall diagonally down and towards the stage.
When you are close to the wall use your double jump and continue holding towards the stage.
Now as soon as you ht the wall press away from it and you should successfully wall jump.
If you wann come back from this you basically have to use your upB or diagonal up air dodge on to the stage.
I hope that helps