Hallo, I am flying Boing 777 professional (I am a beginner and trying to learn). I have programmed the FMC from A to B. Then when I am in the air I must land elsewhere (it´s too foggy or I must do a forced landing). 1. How do I change the arrival airport in the FMC? 2. To make a forced landing perhaps I must descend quickly, then I get an overspeed warning. What is the dangers with that? Or shall I just ignore the warning and proceed?