What else are you doing to lose weight? Not sure how much you have to lose, but doubt that a sauna can do it without adding other healthy choices to your routine, like the right kinds and amounts of food, along with adequate exercise.
I would not consider a sauna a method of weight loss. You would initially have a lower weight but that is because of loss of fluids due to sweating. Once you re-hydrated your weight would be the same. Better to lose weight with healthy eating and exercise.
I agree with what the others have said. A sauna is not a long term weight loss solution and all the weight you do lose is just water weight that will return very quickly, probably almost immediately. You're better off sweating off the pounds in a gym than in a sauna.