Since the physics study is a consecutive bachelor / master program, usually one will continue the in the Master's program physics. Once the last examination has been completed, on can enroll in the Master's program at the registrar's office (Studierendensekretariat).
As an alternative to the Master's program in physics, I am aware of the following Master's programs at RWTH Aachen University (as of 25.02.2019), which accept Bachelor's graduates of physics, but in some cases with restrictions or additional obligations:
Another alternative is the change of university.An overview of Master's programs in physics at other German universities is available at www.hochschulkompass.de (study-> Subject index (continue to study) -> enter "Physik"). The CHE-Ranking may help you in your search for physics departments all over Europe.