Hi, @TR24, your Fitbit will not tell you your ideal weight. If you would like to use it for weight loss a good start would be to choose a weight goal. You can do this on your app. It is up to you to choose your goal, amd this can change over time, so that if you like, you can meet a series on mini goals.
If you are curious about what others might think your "ideal" weight is there are lots of websites that will help you calculate it. I particularly like this one.
Sense, Charge 5, Inspire 2; iOS and Android