It seems like your question would be better placed in the "weight loss" forum. I'll copy it there for you.

You don't, and you shouldn't aspire to such a low weight at your height. Just my opinion. The things you'd have to do to get to that weight would surely prompt an eating disorder, and I speak as someone recovered from anorexia. You don't want to go there. Believe me. It's miserable. And once you get to your super-low goal weight, you'll just keep wanting to get lower and lower. I weighed 80 lb. By the time I got help and i'm lucky I didn't kill myself. I started with a goal weight of 100 lb. At 5' 4". Don't do it is my advice. Just not worth it.

I agree with cln. That would not really be a healthy weight for that height, therefore, there is not really a healthy way to do it. It's one thing if you're just that skinny and always have been without trying. No one could blame you for that. However, to have a weight such as that as your goal sounds dangerous to me. You do not have to be anorexic to have an eating disorder.

with your height, I think your goal should be in the 120s, or even the 130s. Your aim should not be super skinny, but just fit with the right amount of muscles and fat where they are needed. Being in the 100s with your height is dangerous, and I guarantee you that you will not be feeling good when you reach that point, but you will be feeling weak with constant lack of energy.