I'm gonna try to explain this as best I can through text which is pretty difficult but we'll see how it goes.
We can identify beat 1 by listening to where Harry generally starts his vocal phrases. Right a the beginning he sings "Take me home, I'd love to be invited". The words "take" and "i'd" are both on beat 1. Now we have our reference. Count along while listening now if you'd like, it's fun!
The beat switch happens around 0:43 but if we listen to the solo section in general we can dissect it. He plays a repeating bass line with his left hand throughout. It is very audible from 0:50-0:53. He is doing some fancy work in the higher register but the bass line is anchoring it. There is a strong beat in this bass line. You can probably hear it naturally. It is the third note he plays in the sequence. This third note is again beat 1.
The bass line leads into beat 1 like so: "and-a-ONE". Sing along in your head. Now sing along with the bass line as he goes into his solo. You'll notice that right around 0:39 he stops playing the bass line for a moment. This is where he 'corrects' the audience. After this point the "and-a-ONE" of the bass line is no longing in unison with the clapping. If you kept your count going you'll find that it no longer matches the bass line. After he does this the clapping is now on the TWO and FOUR relative to the bass line.
Hope this helps some people. It's pretty damn cool what he did, and so smooth!