How can I loss weight?

I feel healthy and think i look good, but my doctors keep saying I need to loss weight, at some point I gave up but then my parents started to tell me I should listen to the doctors, I weight like 57kg but they tell me base on my height I should be somewhere in 45kg, even tho I tried a lot, I don't loss weight and when I do, it can return some time later.

How can I loss weight?
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