What to do if you don't know what to write in an essay?

This is the approach I often use with my students. (I'm retired now, but it's too weird for me to write about it in the past tense.) Forget for a few minutes that you need to write an essay and think about your topic. What do you think? Say it out loud. Just cough it up. Now write down what you just said, word for word. Now do it again. And again. The trick to figuring out what to write is to figure out what you're thinking about. So think first and take notes as you think, as if you were listening to someone else talk about your topic. Once you have your source material in this way, you can organize your ideas so that they make sense to each other and make a first draft. If that didn't work for you statement of purpose writer   will do all the necessary work for you. And you should rest and try to repeat the procedure, but on a different one.