You can attend an equivalent course during your Master’s. The lecturer of the mandatory course decides which courses are equivalent and you need an equivalence form signed by the lecturer.

In the case of Stochastik 1 you could do the following: 1) show that you attended an equivalent Stochastik 1 course during your bachelor 2) attend e.g. Stochastics 2 and count it as your Stochastik 1 grade in the Master’s programme.