We just did ours in Zürich in May. We live in Kreis 11, so ours is on Nansenstrasse 16 - have a look here to see who the Notary responsible for your area is:
https://www.notariate-zh.ch/deu/notariat/
Once you have found the office whose jurisdiction you come under, send them an email and they will give further instructions.
The next thing that happened after the email was: the Notary gave my then-fiance a ring, to clarify what it is that we wanted in the agreement. At the same time, for us, because I am a non-German speaker, he asked that we engage the service of a certified translator. We did not know of any translator personally recommended to us, so they gave us the contact of one and we contacted her directly.
Once the Notary had a draft of the agreement, he sent it to us and to the translator via email for proofing. And then we agreed on a date for all parties to meet at the Notariat. During the meeting, the translator explained everything in detail to me and helped translate questions/answers before signing by all parties.
The final document is both in English and German, nicely signed and stamped.
Cost was CHF397.70, incl MSWT etc
Hope that helps