Welcome to our community and thank you for your question.
Usually you make an appointment at Bürgeramt in order to do Anmeldung. You have to submit a so-called "Einzugsbestätigung". It's a document that your landlord is obliged to issue for you. It contains the name and address of your landlord, the date you moved in, the address of the apartment that you moved into and your name. It's not sufficient to only provide your lease agreement.
Here you find a list of all Bürgerämter in Berlin. You can pick one that is located close to your current address:
To make an appointment you have to select one of the Bürgerämter and scroll down a bit. The you have to check the box next to "Anmeldung einer Wohnung". After that you click on the button at the bottom that says "An diesem Standort einen Termin buchen".
Unfortunately they are usually fully booked which is why you have to call (030) 115. They will give you an appointment in an Bürgeramt of your choice within 14 days so that you don't miss the deadline.