The way I did it was:
I would stay in a quiet room, with no distractions, no tv, no laptop and no music. I would write down the first sentence. Then recite it to myself out loud. I would do this until I knew it, most of the time I spoke it 5 times and then I could remember it. Once I memorized the first sentence, I would write down the next sentence and remember that. Then I would speak the first sentence combined with the second one. This was effective for me and I have done it for writing and speaking assessments and got an A. If this doesn't work for you then I advise trying to re-write it over and over again until you remember it. Or you could record yourself speaking your assessment out loud, and listen to it whenever you can (this never worked for me because I zoned out every now and then but it could work for you). Good luck with your assessments!