It’s easy as seatching for your microwave model + the keyword “manual”, there’s typically a section on exactly this. If nothing comes up just try a generic search like “How to silence microwave” and find what works.

FYI some microwaves do not have a silence function

I wrote “some code” back when I was a child, if you asked me to explain how it works all I could tell you is “through the power of santa’s little helper”.