You should check out the official guide of the city explaining the whole procedure of registering your address. LifeX only provides your rental contract and H-number, but does not take care of your registration.

Make sure to always put: FULL NAME C/O LifeX in the name field for your address - this way the post will always be able to find you even if you don't have your name on the mailbox.

The H-number can be found on a sticker on he door frame on the studio.