Since sweating is a reaction to excess body heat, the only way to stop it is to shed that heat. That is, you need to stop doing what is creating the excess heat and/or cool yourself off through different means. Cold showers or even running cold water over your wrists or neck will help, but you will sweat until your body normalizes it’s internal temperature.
Some people just sweat more than others and there’s nothing you can really do about it. Losing weight may help but increasing physical fitness may actually increase the rate and onset of perspiration. In the end, sweat is a normal human process. Embrace it and plan for it.