What are the official requirements for extending a visa in Thailand due to COVID-19, and do I need to make an appointment?

Hi all,

I am planning to apply for the extension due to covid. My current stamp runs out on the 21st December. I understand that they've announced that people have until the 29th Jan to do this. My questions are; what are the official requirements? (Documentation), does one need to go to MTT or chaengwattnaa?. I'm a little confused as I've always gone to chaengwattnaa for extensions previously. And finally, is making an appointment essential?.

Apologies if this has been asked before, I just want to get clarity from others who have done it already.

Many thanks!