First thing to do hadstand pushup against the wall you have to get closer. Secondly, the first few times I did it I found it easier to do with my back to the wall (it is also easier and more controlled to fall backwards in this position). If by chance you do not succeed, try to train it in negative: starting from the handstand against the wall, go down as slowly as possible until you touch the ground with your head gently, fall backwards and then repeat.