It’s rent reduction time again! All you need to do is write to your landlord requesting a reduction. The landlord won’t contact you, you need to contact them, and you need to send them a registered/signed for letter within 30 days.
You can use the template letter from the Mietverband or write your own.
Estimated savings are 2.9% on the annual rent - a nice amount to have in your pocket, instead of in your landlord’s.