Stolen phone with authenticator

Question

Hi All.

I had my phone stolen, and it has the Microsoft Authenticator app on it. Thats used for a number of work and personal applications. I've recovered it, but read an article that says I have to actively de-register the old phone, and I cant find out how to do that. The formal Q&A

https://support.microsoft.com/en-gb/account-billing/common-questions-about-the-microsoft-authenticator-app-12d283d1-bcef-4875-9ae5-ac360e2945dd#lost-device

says to go to Account Security, but that doesnt show me devices just methods of access.

I'd like to know how to remove the old phone completely and ensure - if somehow the PIN is compromised - that they won't be able to use the authenticator app.

Help very much appreciated!

Mark