That depends on which step you missed. If you missed the one of the last few steps (Communication/Analysis) it does't matter... you can just do those now. You couldn't have missed the first step, or you wouldn't have an experiment to begin with. The second step is trivial if you miss it (research). If you missed making the hypothesis... I guess write down what you *thought* was going to happen instead of what happened. I have no idea what you are doing if you missed the experiment part though