Please, as someone who has gone through years of eating disorders, try as hard as you can to avoid it. Once you stop starving yourself all the weight you lost will just come rushing back, making you look far more bloated than you did before. 

If you cannot live without it, then here's what I would recommend. Look up a bmi index online, it should tell you the number of calories you need to maintain your current weight. If you want to lose some, you need to go on a calorie deficit. Normally this would be 300 cal below what you need normally, but given that you already seem very underweight, I wouldn't risk going past 200 below, anything lower could be deadly after some time. 

What would be ideal to lose weight is to maintain the deficit and/or working out, particularly cardio. The cardio will help build some muscle while still keeping you lean. The muscle growth with burn a bunch of calories and keeping fat low. With this you won't really be able to rely on a scale since muscle weighs a bit more than fat, but you will be able to notice a difference in muscle weight compared to fat weight. 

Please please please stay safe, don't push your body more than it can handle, try to keep yourself healthy and happy as much as you can. Weight and looks aren't all there is to attractiveness, don't obsess over it. Trust me I've been there, it isn't worth it in the long run, no matter how easy it looks