If you are taking part in a study-preparatory German course, there is no possibility of taking out statutory health insurance for the time being. In this case, your only option is to take out private health insurance.
You will only have the option of taking out statutory health insurance when you start your studies. In this case, it is possible to switch from private to statutory health insurance. If you take up studies in Germany as a privately insured person, you can no longer switch to a statutory health insurance for the entire duration of your studies!
List of private health insurance companies