There is absolutely no possibility that pressing any point, not just KD 1, for a few times would the "next day" change your weight and make you thin. If you did lose weight that quickly it would far more likely be a virus or some other internal issue. While acupressure can be helpful, it's not that powerful.
If you are weak and thin you might do better with moxibustion at ST 36, or if moxibustion is not available, just acupressure there and possibly at KD 3.
But the best results will come from finding an acupuncturist in your local area, having them diagnose your properly and then they can recommend appropriate dietary changes and lifestyle changes and, if applicable, acupressure points that might be useful for you.