Or
B) Get impatient, cut them off and tell them everything you know about the topic?
Or
C) Patiently let them finish, THEN tell them you already know, and everything you know about the topic?
I personally have a tendency to be an impatient douche sometimes so I admit I don’t always handle these situations with the greatest patience & social grace.
A - if I have time listen, look for surprises, if something doesn’t match my expectations or experience ask Socratic questions… Maybe I’ll learn something new. No need to cut them off, just steer the conversation toward interesting areas