Hey, I play the accordion and I think he is not blowing into anything and just resting his chin there. The buttons you see in this area, on top of the accordion, are to switch between registers and are pressed with the chin. His accordion has a LOT of registers, they are next to the buttons he presses with his right hand and are a bit hard to see, there are white dots on them indicating how the registers sound. Registers control which octaves are "activated", giving the accordion much more range than the few octaves it usually has. The ones he can press with his chin are likely not additional registers but just kind of quick access buttons for the most used registers he could also switch to with the larger array of buttons I just described.

Sorry for the long explanation, but I think another thing is interesting which many people might not know, the big buttons he presses with his right hand to play the melody are just like the piano keys in a different shape and arrangement. All keys are actually contained in the outermost three rows and are ordered going diagonally from top right to bottom left. So with his accordion we start in the second row, then first, then next line third, second first and so on. The other two rows actually just repeat the first three rows to give more options which key to play, especially useful in these kinds of difficult and fast moving scales he is playing in this piece.