How do you become truly nothing?

In the changing the boxes meditation he talks about becoming nothing, while I did have interesting experiences with the tape, when he talks about becoming nothing for me that means losing all sense of self including the observer right?

However for me I don’t lose the sense of ‘I’ though I feel it weakness a bit, how do you truly lose your sense of self, including the observer? Is there a different meditation going more in depth about this state? Since changing the boxes is only 20 minutes so I feel it wouldn’t be the best one to access this state.